~Air-conditioning Basics~

An air conditioner is basically a refrigerator without the insulated box. It uses the evaporation of a refrigerant, like Freon, to provide cooling. The mechanics of the Freon evaporation cycle are the same in a refrigerator as in an air conditioner. According to the Merriam-Webster Dictionary Online, the term Freon is generically "used for any of various nonflammable fluorocarbons used as refrigerants and as propellants for aerosols."

Diagram of a typical air conditioner

This is how the evaporation cycle in an air conditioner works (See How Refrigerators Work for complete details on this cycle):

1. The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas (red in the diagram above).
2. This hot gas runs through a set of coils so it can dissipate its heat, and it condenses into a liquid.
3. The Freon liquid runs through an expansion valve, and in the process it evaporates to become cold, low-pressure Freon gas (light blue in the diagram above).
4. This cold gas runs through a set of coils that allow the gas to absorb heat and cool down the air inside the building.

Mixed in with the Freon is a small amount of a lightweight oil. This oil lubricates the compressor.

So this is the general concept involved in air conditioning. In the next section, we'll take a look inside a window unit.

~Air Conditioning~

Just about every modern car, truck or SUV sold these days can be had with air conditioning. It's so common that most people take it for granted. You press the button for air conditioning in your car and — presto! — cold air starts to flow out of the car's vents. It's easy, it's simple, and it's a major convenience. Could you imagine driving to a job interview in Phoenix, Ariz., if your car didn't have air conditioning? By the time you got to your interview, you'd be a sweaty, stinky mess.

Have you ever wondered how the air conditioning in your vehicle works? If you're like most people, you probably haven't. But we're here to educate you painlessly. Air conditioning is the process by which air is cooled and dehumidified. The air conditioning in your car, your home and your office all work the same way. Even your refrigerator is, in effect, an air conditioner. While there are many physical principles that relate to air conditioning, this article sticks to the basics. It explains the general concepts of automotive air conditioning, the components used and what you need to know to keep your car's A/C system working properly.

Did you know that when you turn on the A/C in your car, you are burning extra gasoline to make yourself feel cooler? It's weird to think that by burning something you become cooler, but it's true.

Here's a simple example of evaporation. Imagine that you're swimming around in your neighbor's backyard pool on a summer day. As soon as you get out, you start to feel cooler. Why? The water on your body starts to evaporate and turns into water vapor. And as it evaporates, it draws heat away from your body, and you get goose bumps. Brrr! Now let's say your neighbor hands you a big glass of ice-cold lemonade. You take a sip and set it down on a table. After a minute or two, you notice that water has collected on the outside of the glass. This is condensation. The air surrounding the glass becomes cooler when it encounters the cold glass, and the water vapor the air is carrying condenses into water.

Both of these examples occur at normal atmospheric pressure. But higher pressures can also change a vapor (or a gas) into a liquid. For example, if you look at a typical butane cigarette lighter, you can see liquid inside it. But as soon as you push down on the button, butane gas comes out. Why? The butane is under high pressure inside the cigarette lighter. This high pressure causes the butane to take liquid form. As soon as the butane is released and it encounters normal atmospheric pressure, it turns back into a gas.

OK, those are the basic ideas. But how do they apply to making your car's vents blow cool air? The principles of evaporation and condensation are utilized in your car's A/C system by a series of components that are connected by tubing and hoses. There are six basic components: the compressor, condenser, receiver-drier, thermostatic expansion valve, the evaporator and the life-blood of the A/C system, the refrigerant.

Refrigerant is a liquid capable of vaporizing at a low temperature. In the past, R-12 refrigerant was used in cars. But this chlorofluorocarbon (CFC) is harmful to the earth's ozone layer. Consequently, all vehicles built after 1996 use R-134A, a more environmentally friendly refrigerant.

Here's how an air conditioning system and its components work.

Step One: The compressor is the power unit of the A/C system. It is powered by a drive belt connected to the engine's crankshaft. When the A/C system is turned on, the compressor pumps out refrigerant vapor under high pressure and high heat to the condenser.

Step Two: The condenser is a device used to change the high-pressure refrigerant vapor to a liquid. It is mounted ahead of the engine's radiator, and it looks very similar to a radiator with its parallel tubing and tiny cooling fins. If you look through the grille of a car and see what you think is a radiator, it is most likely the condenser. As the car moves, air flowing through the condenser removes heat from the refrigerant, changing it to a liquid state.

Step Three: Refrigerant moves to the receiver-drier. This is the storage tank for the liquid refrigerant. It also removes moisture from the refrigerant. Moisture in the system can freeze and then act similarly to cholesterol in the human blood stream, causing blockage.

Step Four: As the compressor continues to pressurize the system, liquid refrigerant under high pressure is circulated from the receiver-drier to the thermostatic expansion valve. The valve removes pressure from the liquid refrigerant so that it can expand and become refrigerant vapor in the evaporator.

Step Five: The evaporator is very similar to the condenser. It consists of tubes and fins and is usually mounted inside the passenger compartment. As the cold low-pressure refrigerant is released into the evaporator, it vaporizes and absorbs heat from the air in the passenger compartment. As the heat is absorbed, cool air will be available for the occupants of the vehicle. A blower fan inside the passenger compartment helps to distribute the cooler air.

Step Six: The heat-laden, low-pressure refrigerant vapor is then drawn into the compressor to start another refrigeration cycle.

As you can see, the process is pretty simple. Just about every vehicle's A/C system works this way, though certain vehicles might vary by the exact type of components they have.

The best thing about air conditioning is that all you have to do is press a button to make it work. Air conditioning systems are pretty reliable. On a modern and relatively new vehicle, it is rare to have problems. And if there are problems, they are pretty much one of two things: No cool air or insufficient cool air. If you own an older car and its A/C system doesn't seem to be working properly, here are some general troubleshooting tips:

~No Cool Air~

• Loose or broken drive belt
  
• Inoperative compressor or slipping compressor clutch
  
• Defective expansion valve
  
• Clogged expansion valve, receiver-drier or liquid refrigerant line
• Blown fuse
  
• Leaking component: any of the parts listed above or one of the A/C lines, hoses or seals

~Insufficient Cool Air~

• Low refrigerant charge
  
• Loose drive belt
  
• Slipping compressor clutch
  
• Clogged condenser
  
• Clogged evaporator
  
• Slow leak in system
  
• Partially clogged filter or expansion valve
  

Most A/C repairs are best left to a repair shop. Recharging the refrigerant, in particular, requires special equipment that most people don't own. There are a couple things you can do, however. First, make sure to have the system checked regularly according to your vehicle's owner's manual. Second, if you live in a place with a cold climate, it might not make much sense to run the A/C during the winter months, but many shop technicians recommend running your A/C system regularly, because it contains a light mineral oil in the refrigerant to keep the compressor properly lubricated. The general rule of thumb is 10 minutes per month. Some heating, ventilation and air conditioning systems also engage the A/C compressor for defrost mode (for example, most GM vehicles).


~Pressure Blowers ~



~Unit Heaters ~



FRP-General-Purpose Fume Exhausters

Selecting Air Conditioner Components

Split system air conditioners contain various components that must be matched up accordingly. We have a special Kit Builder to help you select all the right components.

In a split system, the compressor and condenser coil (contained in a standard unit or heat pump), are installed outside the home, and the evaporator coil is installed inside the home in the plenum of a forced-air furnace or air handler. The indoor and outdoor components of a split-system are usually connected by two refrigeration lines and a low-voltage relay cable.

The following components make up a split system:

	Standard Unit (Condenser) or Heat Pump A condensing unit is the main component of central air conditioning, and is the part that sits outside the home. Inside it is a pump called a compressor, coils, fan and electrical system. The condenser comes entirely pre-assembled and pre-charged with Freon. When a standard air conditioning system (with a condensing unit) is operated, the condenser in the yard gets warm and the evaporator coil in the furnace gets cold, thereby cooling the home in summer. With a heat pump, the same happens in summer, but in winter, the reverse occurs: the outside condenser gets cold and the inside evaporator coil inside the air handler gets warm, thereby heating the home. Heat pumps work best in climates where winter temperatures do not regularly fall below 25 degrees Fahrenheit. Most homes in central and northern states use standard systems, and in the south, both standard and heat pumps are popular.
Evaporator Coils An evaporator coil is the part of an air conditioning or heat pump system that becomes cold when the unit operates. It is connected to the ductwork of the home. When the system is on, air flows through the coil and the cold air is distributed throughout the home. Evaporator coils are either cased or uncased and must be matched up with the condensing unit or heat pump to ensure proper operation of your air conditioning system. You will need only one of the following three types:
	Cased Evaporator Coils Cased evaporator coils are used primarily if you are purchasing a new furnace. Cased coils and furnaces sold on our site must be matched up for an exact fit.
	Horizontal Evaporator Coils Horizontal evaporator coils are used when you have a furnace that is mounted horizontally.
	Uncased Evaporator Coils Uncased evaporator coils are used primarily if you already have a furnace and will be inserting the coil in your pre-existing ductwork.
	Condensing Unit Pad Pads are simply a base for the outdoor air conditioner or heat pump to sit on. They are made of 2-inch thick plastic and are very rigid. The plastic is made with ultraviolet inhibitors so it will not break down in sunlight. Pads come in different sizes, fitted for your particular condensing unit or heat pump.
	Electrical Disconnect A disconnect is a safety on/off electrical switch mounted on the home near the condenser or heat pump. It is required by electrical code, and is a good idea for safety and system servicing purposes.
	Refrigerant Line Sets Line sets consist of two semi-flexible copper pipes to connect the outdoor air conditioner or heat pump to the indoor evaporator coil. The smaller pipe is called the liquid line. The larger pipe is referred to as the suction line and includes insulation. The liquid line diameter for all systems is 3/8 inches in diameter. The suction line diameter will be either 3/4, 7/8 or 1 1/8 inches, depending on the size and efficiency of the air conditioner or heat pump. Line sets come in several lengths and are designed to be cut to fit your exact needs.
	Electrical Whips Electrical whips are simply wires in a weatherproof casing for outdoor use. They are used to connect the 220-volt power to your outdoor air conditioner or heat pump. A typical installation requires two electrical whips. Whips come in two wire size thicknesses (gauges), No. 10 Gauge or No. 8 Gauge and are used depending on which system size and efficiency you choose.
	Installation Supplies Packages Alpine Home Air Products Supplies Packages make your air conditioning or heat pump installation easy! They include nearly all the miscellaneous materials needed for the job. If you are using an uncased evaporator coil, choose a supplies package that also contains pre-fabricated sheet metal for a fast and easy coil installation. All supplies packages include our exclusive 1-hour installation instructional video that clearly shows you how to install your own air conditioning system successfully.

~CaR aIr CoNdItIoNiNg SyStEm SeRvIcE~

L V V Services offer a fully mobile vehicle air conditioning Repair and Regas service; we are based in Bridgend, South Wales and cover an area from Newport to Swansea along the M4 corridor and the surrounding area.

Air conditioning system operation

Air conditioning is a system used to create and maintain a comfortable driving environment inside a vehicle. It does this by transferring the heat from inside a vehicle to the outside keeping the temperature down inside the car.The system cools, dries and cleans the air.

The most basic systems have manual temperature control but systems are becoming more and more complex with full climate control on a lot of modern cars which rely on a lot of sensors to maintain the selected temperature.

Air conditioning system schematic diagram-basic system

Common Air conditioning problems

Air conditioning system not cold enough

The Air Conditioning system in your vehicle is not usually covered by most manufacturers servicing schedules and the refrigerant gas that is used to operate the system depletes over time. On average most vehicles lose up to 15% per annum this problem can be caused when then system is not used during the winter months allowing the small “O” ring seals to dry out resulting in a gradual deterioration in system performance eventually resulting in the system being too low to operate at all.

Most problems of this type can be put right fairly easily by a leak check of your system followed by a complete refill of your air conditioning refrigerant, this is sometimes referred to as a re-gas. Please contact us for your air con annual service or re-gas if you live in the Cardiff,Swansea, Bridgend or Newport area.

Air conditioning system smells odd

If you notice any strange smells when you put your air-con on then this could be signs of bacteria build up on your system.

Don’t suffer any longer air con systems can be treated effectively with an anti-bacterial treatment that destroys the bacteria growth and leaves your car smelling fresh again.

Please call for a quote. from one of our mobile air con repair technicians.

Some noises could be early symptoms of a compressor failure (the compressor is the air conditioning pump).The compressor is usually the most expensive part on the system ranging from approximately £230 to £600+ and if the bearings in your compressor break down or if the compressor seizes up it also means that other components can become contaminated with metal particles A flush of the system would then be needed as well as replacement of the compressor, the receiver / drier and the expansion valve - quite a hefty repair bill!

Its not all bad news however - some noises are quite normal

There are 2 different types of air-con system operation some vehicles use a system where the compressor (pump) cycles on and off which means that there is a clicking noise heard every few seconds this is normal, however if this switching cycle changes noticeably or the air con is not very efficient this could be an early symptom of low refrigerant or low gas pressure.

Pool of water underneath the car after using air-conditioning

You will sometimes see a water puddle on the ground, usually under the passenger footwell area, this is a normal feature of the air conditioning system as it is only water dripping from the air conditioning evaporator which has a drain tube fitted to allow the condensation from the evaporator to drain away from the vehicle.

Damp carpet in the footwell or excessive misting of the windscreen

Sometimes the drain tube from the evaporator may become blocked or detached allowing the condensation to build up inside your evaporator if this occurs water will just build up inside your car to a point where there are damp carpets or misting / high humidity type problems.

These are usually fairly easy to resolve. just remember our specialist air con repair technicians are only a phone call away in and around the south Wales area.

Today, as we drive our automobiles, a great many of us, can enjoy the same comfort levels that we are accustomed to at home and at work. With the push of a button or the slide of a lever, we make the seamless transition from heating to cooling and back again without ever wondering how this change occurs. That is, unless something goes awry.

Since the advent of the automotive air conditioning system in the 1940's, many things have undergone extensive change. Improvements, such as computerized automatic temperature control (which allow you to set the desired temperature and have the system adjust automatically) and improvements to overall durability, have added complexity to today's modern air conditioning system. Unfortunately, the days of "do-it-yourself" repair to these systems, is almost a thing of the past.

To add to the complications, we now have tough environmental regulations that govern the very simplest of tasks, such as recharging the system with refrigerant R12 commonly referred to as Freon® (Freon is the trade name for the refrigerant R-12, that was manufactured by DuPont). Extensive scientific studies have proven the damaging effects of this refrigerant to our ozone layer, and its manufacture has been banned by the U.S. and many other countries that have joined together to sign the Montreal Protocol, a landmark agreement that was introduced in the 1980's to limit the production and use of chemicals known to deplete the ozone layer.

Now more than ever, your auto mechanic is at the mercy of this new environmental legislation. Not only is he required to be certified to purchase refrigerant and repair your air conditioner, his shop must also incur the cost of purchasing expensive dedicated equipment that insures the capture of these ozone depleting chemicals, should the system be opened up for repair. Simply put, if your mechanic has to spend more to repair your vehicle - he will have to charge you more. Basic knowledge of your air conditioning system is important, as this will allow you to make a more informed decision on your repair options.

Should a major problem arise from your air conditioner, you may encounter new terminology. Words like "retrofit" and "alternative refrigerant" are now in your mechanics glossary. You may be given an option of "retrofitting", as opposed to merely repairing and recharging with Freon. Retrofitting involves making the necessary changes to your system, which will allow it to use the new industry accepted, "environmentally friendly" refrigerant, R-134a. This new refrigerant has a higher operating pressure, therefore, your system, dependant on age, may require larger or more robust parts to counter its inherent high pressure characteristics. This, in some cases, will add significantly to the final cost of the repair. And if not performed properly, may reduce cooling efficiency which equates to higher operating costs and reduced comfort.

Vehicles are found to have primarily three different types of air conditioning systems. While each of the three types differ, the concept and design are very similar to one another. The most common components which make up these automotive systems are the following:

COMPRESSOR, CONDENSER, EVAPORATOR, ORIFICE TUBE, THERMAL EXPANSION VALVE , RECEIVER-DRIER, ACCUMULATOR. Note: if your car has an Orifice tube, it will not have a Thermal Expansion Valve as these two devices serve the same purpose. Also, you will either have a Receiver-Dryer or an Accumulator, but not both.

For more information on Air Conditioning, check out The Automotive Air Conditioning Information Server

COMPRESSOR

Commonly referred to as the heart of the system, the compressor is a belt driven pump that is fastened to the engine. It is responsible for compressing and transferring refrigerant gas.

The A/C system is split into two sides, a high pressure side and a low pressure side; defined as discharge and suction. Since the compressor is basically a pump, it must have an intake side and a discharge side. The intake, or suction side, draws in refrigerant gas from the outlet of the evaporator. In some cases it does this via the accumulator.

Once the refrigerant is drawn into the suction side, it is compressed and sent to the condenser, where it can then transfer the heat that is absorbed from the inside of the vehicle.

CONDENSER

This is the area in which heat dissipation occurs. The condenser, in many cases, will have much the same appearance as the radiator in you car as the two have very similar functions. The condenser is designed to radiate heat. Its location is usually in front of the radiator, but in some cases, due to aerodynamic improvements to the body of a vehicle, its location may differ. Condensers must have good air flow anytime the system is in operation. On rear wheel drive vehicles, this is usually accomplished by taking advantage of your existing engine's cooling fan. On front wheel drive vehicles, condenser air flow is supplemented with one or more electric cooling fan(s).

As hot compressed gasses are introduced into the top of the condenser, they are cooled off. As the gas cools, it condenses and exits the bottom of the condenser as a high pressure liquid.

EVAPORATOR

Located inside the vehicle, the evaporator serves as the heat absorption component. The evaporator provides several functions. Its primary duty is to remove heat from the inside of your vehicle. A secondary benefit is dehumidification. As warmer air travels through the aluminum fins of the cooler evaporator coil, the moisture contained in the air condenses on its surface. Dust and pollen passing through stick to its wet surfaces and drain off to the outside. On humid days you may have seen this as water dripping from the bottom of your vehicle. Rest assured this is perfectly normal.

The ideal temperature of the evaporator is 32° Fahrenheit or 0° Celsius. Refrigerant enters the bottom of the evaporator as a low pressure liquid. The warm air passing through the evaporator fins causes the refrigerant to boil (refrigerants have very low boiling points). As the refrigerant begins to boil, it can absorb large amounts of heat. This heat is then carried off with the refrigerant to the outside of the vehicle. Several other components work in conjunction with the evaporator. As mentioned above, the ideal temperature for an evaporator coil is 32° F. Temperature and pressure regulating devices must be used to control its temperature. While there are many variations of devices used, their main functions are the same; keeping pressure in the evaporator low and keeping the evaporator from freezing; A frozen evaporator coil will not absorb as much heat.

PRESSURE REGULATING DEVICES

Controlling the evaporator temperature can be accomplished by controlling refrigerant pressure and flow into the evaporator. Many variations of pressure regulators have been introduced since the 1940's. Listed below, are the most commonly found.

ORIFICE TUBE

The orifice tube, probably the most commonly used, can be found in most GM and Ford models. It is located in the inlet tube of the evaporator, or in the liquid line, somewhere between the outlet of the condenser and the inlet of the evaporator. This point can be found in a properly functioning system by locating the area between the outlet of the condenser and the inlet of the evaporator that suddenly makes the change from hot to cold. You should then see small dimples placed in the line that keep the orifice tube from moving. Most of the orifice tubes in use today measure approximately three inches in length and consist of a small brass tube, surrounded by plastic, and covered with a filter screen at each end. It is not uncommon for these tubes to become clogged with small debris. While inexpensive, usually between three to five dollars, the labor to replace one involves recovering the refrigerant, opening the system up, replacing the orifice tube, evacuating and then recharging. With this in mind, it might make sense to install a larger pre filter in front of the orifice tube to minimize the risk of of this problem reoccurring. Some Ford models have a permanently affixed orifice tube in the liquid line. These can be cut out and replaced with a combination filter/orifice assembly.

THERMAL EXPANSION VALVE

Another common refrigerant regulator is the thermal expansion valve, or TXV. Commonly used on import and aftermarket systems. This type of valve can sense both temperature and pressure, and is very efficient at regulating refrigerant flow to the evaporator. Several variations of this valve are commonly found. Another example of a thermal expansion valve is Chrysler's "H block" type. This type of valve is usually located at the firewall, between the evaporator inlet and outlet tubes and the liquid and suction lines. These types of valves, although efficient, have some disadvantages over orifice tube systems. Like orifice tubes these valves can become clogged with debris, but also have small moving parts that may stick and malfunction due to corrosion.

RECEIVER-DRIER

The receiver-drier is used on the high side of systems that use a thermal expansion valve. This type of metering valve requires liquid refrigerant. To ensure that the valve gets liquid refrigerant, a receiver is used. The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt. The receiver-drier usually has a sight glass in the top. This sight glass is often used to charge the system. Under normal operating conditions, vapor bubbles should not be visible in the sight glass. The use of the sight glass to charge the system is not recommended in R-134a systems as cloudiness and oil that has separated from the refrigerant can be mistaken for bubbles. This type of mistake can lead to a dangerous overcharged condition. There are variations of receiver-driers and several different desiccant materials are in use. Some of the moisture removing desiccants found within are not compatible with R-134a. The desiccant type is usually identified on a sticker that is affixed to the receiver-drier. Newer receiver-driers use desiccant type XH-7 and are compatible with both R-12 and R-134a refrigerants.

ACCUMULATOR

Accumulators are used on systems that accommodate an orifice tube to meter refrigerants into the evaporator. It is connected directly to the evaporator outlet and stores excess liquid refrigerant. Introduction of liquid refrigerant into a compressor can do serious damage. Compressors are designed to compress gas not liquid. The chief role of the accumulator is to isolate the compressor from any damaging liquid refrigerant. Accumulators, like receiver-driers, also remove debris and moisture from a system. It is a good idea to replace the accumulator each time the system is opened up for major repair and anytime moisture and/or debris is of concern. Moisture is enemy number one for your A/C system. Moisture in a system mixes with refrigerant and forms a corrosive acid. When in doubt, it may be to your advantage to change the Accumulator or receiver in your system. While this may be a temporary discomfort for your wallet, it is of long term benefit to your air conditioning system.

~IR CONDITIONING FILTERS - Air Conditioning Filter Location, Condition, Problems, Repairs~

First locate and document the placement of the HVAC system air filters - for examination and regular changing during the cooling season.

In our photo at left you can see a blue and white electrostatic air cleaner on the air handler.

But notice at the upper left of the photo just below the brown metal of the air handler body: see that silver sheet metal handle? Removing the two screws on either end of the pull-out will permit you to expose another air filter that is in this location - the handle is a tip-off that the air handler is meant to be opened at this location in order to remove/replace an air filter.

Are these the only two air filters on this system? Nope. Our discussion of cascaded air filters found at OPTIMUM INDOOR AIR FILTERS includes photos of a front-end air filter found at the return air register. In sum, finding a filter on a duct system or air handler is no promise that it's the only air filter installed. Inspect the system thoroughly. If more than one air filter is provided, document the location of all of the filters installed.

Next inspect the air conditioning filter type and condition. What about filters that are missing completely or are very dirty? What problems can a dirty or blocked air conditioner filter cause for the air conditioning system and how do we fix these snafus? That's what we'll cover in this article.

~Air conditioner filter location: filters should be readily accessible~

Filter accessibility: Air filters which are hard to access are rarely changed as often as necessary. I frequently see HVAC systems designed by someone who obviously has never had to service them.

Placement of filters and air handler access doors in very hard-to-access locations such as at the far end of a minuscule attic behind a forest of trusses means that the system is very unlikely to receive the periodic inspection and maintenance it needs.

I prefer to see A/C and heating filters placed at the building side of the air return register or grille, so as to protect the return duct from debris accumulation. The more common filter placement on many systems is right at or in the air handler.

After reading the text just below, if you still cannot find your heating or air conditioning system air filter read our detailed instructions on how to find air filters in our article: Air Filter Location

• At the central air return register, grille located in a wall or ceiling if your system uses centralized air returns instead of individual room-air return ducts. There may be several central return points, depending on the design of your system. If there are more than two, chances are the filter was placed at the air handler instead of at these grilles. Unfortunately that means that the return ducts themselves become more soiled with dust and debris from the building.
  
  
• At an attic air handler look for a slot which has a removable cover. The slot may be just an inch or so wide if 1" thick filters are used, or it could be several inches wide if a wide high-capacity pleated or similar filter was used. The return air plenum on an attic or basement air conditioner blower unit will usually be a large metal enclosure about the same dimensions in width and height as the air conditioner blower unit itself. Look for a filter slot right where the return plenum contacts the blower fan assembly.
  
  
• At a basement air handler we also look for a filter at the return air plenum which is often next to the bottom of the air handler if the system is an "up-flow" unit (or vice versa for the less common case of return air entering at the top of the air handler and exiting at its bottom).
  
  
• Next to an electrostatic air cleaner: if your air conditioning air handler has an electrostatic air cleaner installed, look for the filter, if there is one, next to the electrostatic air cleaner. In addition, the electrostatic air cleaner, which is a type of particle incinerating filter itself, needs to be removed and cleaned periodically. (Check with your unit's manufacturer for cleaning interval and procedures. Often the electrostatic unit can be cleaned inside a dishwasher). Often there is also a thin metal washable air filter installed along with the electrostatic air cleaner.

Change your air filters every month when the air conditioning system is in operation. Make sure you find all of the filters as some systems have multiple filters and even multiple types of filters installed, such as a fiberglass or pleated paper filter, a washable filter, and an electrostatic air cleaner. These last two are cleaned, not replaced, when they're dirty.

~Dirty Air Conditioner Filters Cause Multiple Problems for an Air Conditioning System~

Dirty Air Filters: are a source of increased operating costs and poor cooling system operation. Dirty air filters can: reduce air flow in the building cause dirt to accumulate on the fan blades, wasting your energy dollars cause excessive dirt build-up inside the duct system, leading to mold or allergen problems in a building and to the need for more costly duct cleaning or replacement block the cooling coil itself with dirt, reducing system effectiveness and possibly leading to costly repairs lead to frost build-up on the cooling coil and reduced or totally blocked air flow in the system eventually permit dirt to bypass the filter where it soils and blocks the blower fan itself, leading to more costly repairs. The filters on an air conditioning or hot air heating system should be changed monthly when the system is in use. Discuss with your heating/cooling service professional the possible need to clean the blower fan and duct work.

~Improperly-Fit or Wrong Sized Air Filters Cause Bypass Leakage~

Bending over the end of an air conditioner or heating air handler filter such as shown in the photo at left above is a bad idea. If the filter does not fit there will be bypass leakage past the filter, soiling the blower fan, slowing air flow, and leading to more costly cleaning and service later.

Furthermore when you bend the filter as this owner did, you interrupt the structural integrity of the filter's frame, risking filter collapse. A collapsed air filter can be drawn right into the blower fan, causing damage to the fan motor or even leading to a fire!

The photo at right shows how a college HVAC maintenance crew kept the A/C system running when the school did not have the proper filter size in stock. This filter installation also will have severe bypass leakage around the filter where the pleated section contacts the edges of the filter slot.

Installing a filter that is the wrong size for the heating or air conditioning air handler defeats the purpose of air filters because of leakage and it may be unsafe. Install a properly-sized filter in locations like this as soon as possible and watch out for unsafe filter collapsing.

~How to Construct or Obtain Large or Special-dimension HVAC System Air Filters~

The same college HVAC maintenance staff who was struggling with improperly-fit air filters we discussed earlier was also faced with the task of coming up with a much larger air filter for the air conditioner air handler over their computer center. The neatly-taped "built-up" air filter shown in this photo was nicely constructed but we don't recommend this practice: The filter may come apart and send fragments into the blower assembly, damaging the blower or leading to overheating and a fire. The filter is not delivering the total cross-section of filtering area that was anticipated by the HVAC design engineer who specified the dimensions of the return air plenum at which this filter was installed - we're seeing less total CFM of airflow.

Air filter suppliers and manufacturers have no trouble providing air filters of special dimensions. Furthermore if the filter is built by a manufacturer it's more likely that they'll understand the structural and strength requirements of the filter as well as the required airflow characteristics and filtering ability. We list some suppliers of air filters at SOURCES FOR AIR FILTERS

Incidentally, except unusual cases with special requirements, wouldn't it have made sense for the HVAC or duct system designer to have specified a filter that is one of the many standard sizes?

~Missing Air Conditioner Filters~

Look closely at this photograph. On the right we can see a tan "Air Filter Cover" plate which marks the intended location of the HVAC air filter. But there is an open slot to the left of the air filter cover, possibly where another filter was previously being installed. When the new air filter slot was constructed and nicely covered (so as not to leak) the old slot was simply left open. You can see my piece of adhesive tape bending into the opening, demonstrating (not too scientifically) that there was airflow into the unit from this location. This is a great way to draw attic insulation fiberglass into the air handler and to blow it into the living area. And of course any other unwanted attic dust and debris is also being invited into the air handling system and blown into the occupied space. Failure to properly filter dust from the return air supply will load the fan and cooling coil, dirty the duct system, and lead to the problems listed above. As the ductwork debris level increases you increase the risk of forming an allergen or mold reservoir, especially if there are water or condensate leaks into the duct system interior. If a filter is not present, have one installed. Installing a filter is normally a minor expense. Duct cleaning or duct replacement can be a significant expense. Cleaning up a moldy HVAC system, where mold may have been caused by coil icing which was caused by a dirty coil or filter is still more costly. What are the Components of the Outdoor Portion of a Central Air Conditioning System - the Air Conditioning Compressor Unit? The (usually) outdoor half of a typical air conditioning system is a unit containing the refrigerant compressor and condensing coil. The compressor draws refrigerant gas from the building's inside components, and compresses the gas to high pressure. The condenser coil then cools the high pressure high temperature gas to a liquid state. The heat produced in these steps is transferred to the outside by a fan which blows outside air across the condensing coil. The liquid refrigerant is then able to return to the indoor components for cooling and dehumidifying the building interior. The diagnosis and repair of various defects in the air conditioning compressor/condenser unit are discussed in detail using the links provided at the left of this page. Here is a little more detail about the components of the compressor/condenser unit: The Air Conditioning Compressor Itself - on residential units the A/C compressor motor is most often a hermetic motor-compressor combined in a single sealed unit like the Carrier(TM) unit shown at above left. If a ductless split-system is installed an outside compressor unit is still required, typically looking like the Sanyo(TM) unit shown at the top of this page. The compressor is a basically a pump which moves refrigerant gas to the compressor via the larger refrigerant "suction line" returning it from the in-building air handler and evaporator coil. The compressor compresses the refrigerant to a high pressure gas and moves that gas into the condensing coil described just below. The refrigerant gas leaves the compressor at high pressure and at high temperature (since compressing a gas will raise its temperature.) Refrigerant lines: the larger diameter refrigerant suction line connects the indoor evaporator coil outlet to the compressor inlet. The smaller-diameter high pressure refrigerant lines connect the compressor outlet and the condensing coil inlet and also move refrigerant liquid in it's cooled, condensed and now liquid state from the outlet of the condensing coil to the thermal expansion valve (basically a refrigerant metering device) and the evaporator coil inlet in the air handler unit in the building. Service valves or ports are usually present on the refrigeration lines near the compressor. to permit testing the condition of the air conditioning system and permit removal, replacement, or additions to the refrigerant in the system. Condensing coil receives high pressure refrigerant gas from the compressor and cools this refrigerant gas back to a liquid state. Outdoor cooling fan moves outdoor air across the condensing coil to cool it and assist in condensing the high pressure, high temperature refrigerant gas back into a liquid. It is this process which completes the transfer of heat through the refrigerant from indoor air to outdoor air as the compressor/condener unit compresses and then cools the refrigerant back to a liquid. Electrical shut-off switch(es) for service at the unit are provided to permit maintenance and repair of the equipment. Circuit breaker(s) at the electrical panel protect the circuit supplying power to the air conditioning system. These components are discussed in detail throughout this website using the links at the left of these pages. ~Minimum Air Conditioner Compressor Unit Observations for an Air Conditioner Report~ The compressor and fan operated normally. The rated cooling capacity, estimated age and general condition of the unit are reported below. OR ... We did not operate this equipment because ... so you should ... .

Critical Defects in Air Conditioning Equipment Inspections

Critical defects which an inspector should not fail to detect when examining any building component or system are defects which form an immediate, significant safety hazard or defects which are quite likely to involve significant repair or replacement cost, and which involve components or systems which are necessary to occupy and use the building. Methods for detection and diagnosis of these defects are discussed in this document and in its references. Suggestions for inclusion or exclusion of items in this list are invited - see the link "Contact Us".

• Function: Air conditioning compressor needs replacement
• Function: Cooling is delivered to only part of the building, e.g. only to one floor.
• Safety: Unsafe return air intake which may draw in carbon monoxide at heating equipment
• Uneven air supply resulting in uneven temperatures especially on the first floor of a two story house with ductwork between the first and second floor.
• Inadequate cooling capacity for building.
• Low temperature split (indicating inadequate cooling due to refrigerant leak)
• Refrigerant leaks at condenser or evaporator coils (usually requires replacement of coil.)
• Dirty air handler. (Major expense to clean properly.)
• Leaking return ducts in crawl space
• Safety: Unsafe electrical wiring: aluminum branch circuits and FPE Stab-Lok or Zinsco circuit breakers may have been used to power the compressor. Look for evidence of overheating or over fusing at the service cutoff and in the electrical panel and at the service cutoff by the compressor/condenser [This item is not agreed-on as a critical defect by all reviewers]

  CONDENSATE TRAY CLEANING - Cleaning suggestions for A/C System Condensate Systems

  Should we disinfect cooling system equipment or condensate trays?

  Should we be putting bromide or chlorine tablets in our condensate trays to keep bacteria from growing?

  If we should be, then do we need to alternate bromide with chlorine on some type of frequency to prevent development of resistant bacteria?

  We're discussing condensate trays from mechanical equipment like heat pumps, fan coil units and air handlers with AC coils.

  These pieces of equipment have condensate trays which are then drained through a small pipe, usually clear, but not always, with a trap in it, to a drain.

  These condensate trays have some standing water in them when the AC is functioning. Should these condensate trays be treated with an algaecide of some sort?

  There are risks beyond mold and algae, in particular Legionella bacteria (legionnaire's disease) which can have an alarmingly high mortality rate, and also potential hazard sources such as biofilms that can include other bacterial and maybe other pathogens. However the risk of formation of problem levels of mold, bacteria, or other pathogen is probably not the same across all buildings nor types of equipment, and much of the risk may depend on installation and maintenance details at individual installations.

  Particularly in climates with a high humidity and a heavy cooling load, and depending on details of the design and installation of the air handler unit and duct work, there is risk of blowing pathogen-contaminated water droplets downstream inside the air conditioning duct work and thus exposing building occupants. With rooftop-mounted cooling units such as cooling towers using water, conditions may be still more attractive for growth of pathogens and there is some risk of movement of pathogens out of the cooling equipment to people located nearby and downwind from the equipment, even if they are outside the building which the equipment actually serves.

  While I am not expert on this topic I have collected and provide here some key information and opinions to help sort out these questions. Use the links at page left to read additional details on this topic including recommended cleaning procedures and details of the Leginella hazard in air conditioning systems, humidifiers, etc.

  1. A/C COMPONENT LIST - Basic Air Conditioning Components Inspection List

  Conventional cooling systems include the following components:

  The air conditioning system (and heat pump) components introduced here are discussed in detail and are illustrated by photographs and drawings throughout this website using the links at the left of these pages. We explain how to inspect, diagnose, repair, or select, purchase, and install air conditioning systems or their individual parts and components.

  List of Indoor Components of an Air Conditioning System

• Air Handler Unit (AHU) (shown at left above) which typically includes the following
• Condensate system: water, or condensate is produced when we cool warm moist air by blowing it over the evaporator coil. The condensate runs down the coil to a collecting pan which drains to piping used to route condensate to an approved drain for disposal
• Condensate pump on some air conditioning systems a small pump is used to collect and then pump condensate up to a building drain or other location for disposal. Condensate pumps are needed for systems which cannot dispose of the condensate by simple gravity flow down a drain line.
• Condensate overflow pan or tray is a container placed below the air handler when that unit is located in an attic or in other building locations where condensate leakage or overflow would otherwise spill onto building floors or into a building ceiling. The condensate overflow pan is a safety device intended to prevent unwanted spillage; normally it does not contain condensate. The condensate overflow pan should have either an independent drain to an approved location or a float switch to shut down the air conditioner should the pan become full.
• Blower fan in a blower compartment circulates building air into itself from the return ducts and return plenum, and moves that air across the evaporator coil and onwards to the supply plenum and supply ducts in the building. Blowers may be single speed, multiple speed, or variable speed, and may need to move air at different rates if the blower is used for both heating and cooling in the same duct system. Some air blowers are also rated for continuous operation.
• Electrical controls for an air conditioning system include shut-off switch(es) for service at the unit and fuses or circuit breaker(s) at the electrical panel. The fuse or circuit breaker protects the air conditioner circuit from overheating due to an overcurrent or other electrical failure.
• Evaporator Coil (also called the "cooling coil" is connected to high pressure and low pressure (suction) refrigerant lines. High pressure refrigerant liquid, released into the cooling coil by the thermal expansion valve changes state from a liquid to a gas, causing a drop in temperature of the refrigerant and thus cooling the evaporator coil so that when we move air across the coil the air will, in turn, be cooled.
• Return Plenum, connected to return duct system, is the air receiving compartment which provides air to the blower fan.
• Supply plenum connected to supply duct system, is the air collecting compartment to which building supply ducts are connected. Think of the return plenum and supply plenum as junction boxes to which return ducts or supply ducts respectively can be connected.
• Support system is the means by which an attic-mounted air handler is supported or held in place, for example by being suspended from the roof rafters (a quiet installation) or perhaps by being placed on supporting wood beams laid across ceiling joists.
• Thermal expansion valve: an air conditioner thermal expansion valve is a device located at the cooling coil and connected between the incoming refrigerant line and the refrigerant inlet to the cooling coil in the air handler. The air conditioning system thermal expansion valve or "TEV" is a metering device which regulates the flow of refrigerant from the incoming high pressure side (from the compressor/condenser) into the low pressure side (in the cooling coil). This valve maintains the pressure difference (high and low) at the entry point to the cooling coil, thus assuring that as the high-pressure refrigerant enters the low pressure space of the cooling coil, it can "evaporate" from a refrigerant liquid to a gaseous form, thus producing the temperature drop that cools the cooling coil itself. (All cooling systems using refrigerants use some type of expansion valve, of varying complexity. Even a simple window air conditioner or a refrigerator make use of an expansion valve, in the form of a small-diameter capillary tube or "cap tube" which meters refrigerant into the cooling coil.)
• Air Filters located at the return duct air inlets, at one or more central return air inlets, or at the air handler unit itself are used to remove dust and debris from building air.
• Access ports to duct interior Commercial ducts and some residential duct systems may have inspection/cleaning access ports; residential HVAC ducts may have plugs indicating that the ducts have been cleaned in the past.
• Ductless air conditioning systems, which may also be called "split A/C systems" may employ one or more wall mounted cooling units such as shown at right above
• Return air ducts and registers collect warm moist air from the occupied space and return it to the air handler unit. Some air conditioning installations do not provide return air registers and ducts in every room and use one or more "central air return inlets" instead. Central air returns are most common on air conditioning retrofit installations (adding A/C to an existing building).
• Supply air ducts and supply air registers deliver cooled air to the occupied space. Supply registers have the dual function of spreading out and directing the air flow into a location and permitting the regulation of air flow by opening or closing the register. Some air conditioning duct systems use small-diameter, "high velocity" ducts to deliver conditioned air to the living space.
• Supply air balancing dampers, manual and motorized zone dampers may be installed inside the supply ducts at varying locations in to permit balancing the air flow among different duct sections and thus among different building areas.
• Thermostat(s) are used to turn the air conditioning on and off and to set the desired indoor temperature. One thermostat will be located in each different air conditioning zone and will control an individual air handler unit's operation.

These components are discussed in detail and are illustrated by photographs and drawings throughout this website using the links at the left of these pages.

CONDENSATE HANDLING - Air Conditioning Condensate Handling Defects

Improper handling of air conditioning system condensate is one of the most commonly reported set of A/C system defects, perhaps in part because these defects are easily observed visually, and perhaps also because some A/C installers do not follow basic plumbing and building code requirements for handling the discharge of the condensate produced when an air conditioning system is operating. Condensate leaks or discharge errors (such as the drips into the dog bowl and cooking pot in this attic) present several risks of ugly surprises in buildings including:

First locate and document where condensate discharge is carried

• a plastic line draining outside.
• a floor drain
• a sump pit
• a hole in the floor
• a reservoir lift pump which pipes condensate to: (a properly connected building drain; something else)
• the pump exit line is taken to the house main waste line
a dirt floor or crawl space

Look for corrosion or water stains on floor surfaces around the equipment, at the condensate drip pan and at bottom of the "A frame" cooling coil, indicating that the drain may need cleaning and more important, indicating that the condensate is leaking out of the equipment or drains and not being carried to an acceptable disposal point.

List of Outdoor Air Conditioning System Components

1. Compressor motor - on residential units this is normally a hermetically-sealed motor-compressor combined in a single unit like the Carrier(TM) unit shown at above left. If a ductless split-system is installed an outside compressor/condenser unit is still required, typically containing the very same functions but perhaps more compact, looking like the Sanyo(TM) unit shown at above right. An air conditioning compressor is a specialized pump which draws refrigerant gas back to the compressor/condenser unit from the in-building air handler and evaporator coil. The compressor compresses the returning low-pressure refrigerant gas to a high pressure (and high temperature) form. In a "split" air conditioning system, multiple indoor evaporator coils and blower units may be served by a single outdoor compressor unit such as the Sanyo unit shown at the top of this page. That unit was handling the compressor/condenser function for two wall-mounted, ductless indoor cooling units, one of which is shown in the right hand photo at "List of Indoor Components" above. Split systems like this do not make use of ductwork.
2. Condensing coil receives high pressure refrigerant gas from the compressor and cools this refrigerant gas back to a liquid state.
3. Electrical controls: shut-off switch(es) for service at the unit are provided to permit maintenance and repair of the equipment. Circuit breaker(s) at the electrical panel protect the circuit supplying power to the air conditioning system.
4. Fan an outdoor cooling fan in the compressor/condenser unit moves outdoor air across the condensing coil to cool it and assist in condensing the high pressure, high temperature refrigerant gas back into a liquid. It is this process which completes the transfer of heat through the refrigerant from indoor air to outdoor air as the compressor/condenser unit compresses and then cools the refrigerant back to a liquid.
5. .

   Refrigerant lines: these pipes, typically made of copper, include a low-pressure "suction line" which returns low pressure refrigerant gas from the indoor evaporator coil (cooling coil) outlet to the outdoor compressor motor inlet. The high pressure refrigerant line connects the compressor outlet to the outdoor condensing coil inlet (gas) and further connects the condensing coil outlet to the indoor thermal expansion valve which meters high pressure refrigerant into the "low-side" evaporator coil (cooling coil) in the air handler unit in the building.



Service valves or ports are usually present on the refrigeration lines near the compressor. These valves permit testing the condition of the air conditioning system and permit removal, replacement, or additions to the refrigerant in the system. This photograph of a split system compressor/condenser outdoor unit shows four refrigerant lines and their sets of service ports. The larger diameter copper pipes are the low pressure or suction lines and the smaller diameter pipes are the high pressure lines returning refrigerant to the indoor cooling units. The screw caps visible at the piping connectors where they enter the unit can be removed to provide access to special connecting valves to which the service technician can connect her set of gauges to measure system operating pressures on these lines.

Do not mess with these refrigerant service ports unless you're a trained A/C service technician. You may lose refrigerant or contaminate the system, leading to improper system operation or a costly service call.

~OPERATING CONTROLS - Air Conditioning System Operating Controls~

Basic air conditioning inspection and inspection report information for A/C controls:

1. Thermostats: The air conditioning system is operated by thermostat in the living area. If multiple air handling units and compressors are installed you should find a thermostat for each area served by that equipment.
2. Air conditioning system zone dampers: Some air conditioning system designs may use a single air handler and compressor, but may add zone dampers in the duct work to provide individual "zoning" of cool air distribution. In this case each zone thermostat both calls for the system blower/compressor to operate and also causes a motorized zone damper to open to direct cool air to a particular portion of the building. An ordinary home inspection is unlikely to address proper operation of motorized zone dampers.
3. Manual duct dampers may also be present in duct work to manually balance air distribution among building areas. Be sure to look for these when diagnosing poor cool air delivery to an area.) Also see our note below about the presence of multiple switches and controls.
4. Electrical switches for air conditioning systems will often be found as follows: (some of these may be absent on some systems)
• Electrical panel circuit breakers or fuses will be provided separately to control the air handler (blower system) circuit and the compressor/condenser circuit. Of these the compressor is usually supplied by a 240V circuit and the air handler by a 120V circuit.
• Compressor safety shut off switch outside at the compressor/condenser. The switch may be a circuit breaker, fuse, or a simple "pull-out" disconnect located close to the compressor.
• Air handler service switch inside on or close to the air handler unit itself

  ~SAFETY CONTROLS - Air Conditioning Automatic Safety Controls - Cooling System Fuse or Circuit Breaker Size Requirements~

  ~Electric Power Controls - Safety Disconnects for Air Conditioners~

  Safety disconnects should installed outside next to the compressor/condenser unit and are often also installed next to or mounted on the air handler/blower unit.

  If you cannot find an outside electrical disconnect one should be installed. These controls are recommended for safety to reduce the temptation to open the cabinet and work on the equipment with power on. Working on electrically "live" cooling equipment risks both shock and mechanical injury such as being cut by the fan if the motor starts unexpectedly. Safety shutoffs are required for new equipment.

  ~How to Specify the Breaker or Fuse Size for Air Conditioning Circuits~

  Amperage rating of safety disconnects and A/C circuit breakers: the safety switch on newer equipment may be a simple pull-out fuse-block type power disconnect, leaving circuit protection to be provided only at the circuit breaker or fuse for the A/C circuit where it originates in the electrical panel. Where the actual overcurrent protection is provided (at older circuit breakers used as auxiliary safety disconnects at the equipment, and at the main panel at the origin of the cooling circuit for the compressor/condenser unit) electrical overload protection size (circuit breaker or fuse amperage rating) for modern A/C equipment is specified by the manufacturer.

  The Maximum Fuse or HACR type Breaker: specifies the maximum overcurrent protection or MOP to be used to protect the equipment. The permitted ampacity of the equipment electrical circuit protection (fuse or circuit breaker amps) expressed as MOP or Maximum Overcurrent Protection. If MOP is specified, the breaker or fuse protecting the equipment should match this number.

  As we explained at the beginning of this document, a hermetic compressor draws varying amounts of current (measured in amps) as its internal pressure changes during operation. We said that current draw is higher when starting the motor than when the system is in steady state operation. Current draw is highest if the motor is starting against its highest back pressure such as if the air conditioning system has been turned off and then back on in the middle of operation. Because fusing an air conditioning compressor at the minimum level can result in blown fuses or tripped breakers during these intervals of heavy current draw during compressor startup, compressors are either protected by a slow-blow fuse or a somewhat larger than minimum circuit breaker.]

  Rules of thumb for over sizing air conditioning system breakers or fuses: On some older equipment MOP is not specified. Only when MOP has not been specified can the overcurrent protection required be determined by alternative means such as [RLA OR BCSC whichever is greater x 175%], or if the compressor keeps tripping that device or blowing that fuse, RLA x 225% might be used. The National Electrical Code (NEC) specifies the degree to which a breaker or fuse may exceed the RLA. [For example, if the MOP or fuse size is specified by the manufacturer to be 40 amps, then a 40 amp breaker must be installed with no increase or change in that rating.]

  Multiple switches are often present on cooling systems. As we reminded in the previous chapter, if the air conditioning system won't run, before requesting a service call check all of the switches as well as the thermostat for proper settings.

  ~Air Conditioner Fuse or Circuit Breaker Size Details~

  Generally, what is the ampacity we see in the field when inspecting an air conditioning compressor circuit?

  When the air conditioning system is running, if you measured the amperage, it would be roughly 80% of the RLA. The breaker size is typically about 125% of the total of the compressor RLA and the condenser fan FLA (full load amperage).

  The rationale is that the circuit breaker protecting the air conditioner compressor unit should trip in the event of a locked rotor [the revolving axle of a compressor motor, for example] or some significant electrical event, but should not trip during start up loads which, as we know can be significantly higher than the RLA momentarily [as the compressor motor draws higher amperage to get itself started].

  Why can we put an "oversized" fuse or circuit breaker on an air condtioning compressor circuit?

  An air conditioning electrical circuit is different than a general household circuit in that we have a known current load. [There is only one device connected to the air conditioning electrical circuit, and we can read its operating characteristics.] We are not worried about an overload situation where people plug several appliances into receptacles on a single circuit. Generally speaking, the amperage draw is fine or is way too big.

  Section E3602.10 of the IRC says, "Branch circuits for air conditioning and heat pump equipment. The ampacity of the conductors supplying a multimotor and combination load equipment shall not be less than the minimum circuit and capacity marked on the equipment. The branch-circuit overcurrent device rating shall be the size and type marked on the appliance and shall be listed for the specific purpose." In short, do what it says on the dataplate.

  ~How to Diagnose & Repair an Air Conditioner Compressor Which has Lost Cooling Capacity~

  A compressor which appears to have lost cooling capacity can be diagnosed by a service technician who can connect the appropriate test gauges to the system. Lower than normal discharge pressure and higher than normal suction vacuum will indicate this problem. But before assuming that something is wrong with the air conditioning compressor, some basic investigation is in order. Unless there is an obvious indication of a compressor problem (noise, hard starting, compressor won't start), the service technician, to be thorough and economical, will inspect the system in an order, checking the easy and least-costly problems first, such as presence of electrical power, proper setting and operation of system controls, condition of filters, condition of duct work, operation of blower fans, before moving on to check the compressor itself by looking at the air conditioner operating temperatures, pressures, and current draw in Amps.

  ~Cooling Capacity of the Air Conditioning Equipment~

  The cooling capacity of an air conditioning equipment refers to the ability of the compressor/condenser (usually outside) and the air handler/evaporator (usually inside) to deliver cool air to the occupied space. Briefly, the compressor/condenser draws refrigerant gas from the building air handler, compresses it and cools it back to a liquid refrigerant, and the air handler/evaporator coil permits liquid refrigerant to evaporate inside a cooling coil, across which the fan blows building air to cool and dehumidify it. The particular combination of this equipment has a cooling capacity, usually rated in BTUh or thousands of BTU's of cooling capacity per hour, documented on equipment data tags discussed above at "RATED COOLING CAPACITY" - see links at left.

  ~Air Conditioner Long "on" cycle and Insufficient Cooling - Loose or Worn Compressors~

  A longer than normal "on" cycle combined with little or no cool air conditioner output could be due to an inefficient air conditioning compressor or one which has lost its ability to "compress" the refrigerant due to internal wear. This condition can be diagnosed by an air conditioning service technician who will install air conditioning manifold gauges onto the system to check the compressor suction vacuum and discharge or "high side" output pressure. If gauge ports are not installed on the air conditioner compressor unit the technician cannot make this test without cutting the refrigerant lines to install gauge ports (adding to the cost of this diagnosis).

  ~Low air conditioner motor amperage draw~

  Low amperage draw: unlike a high-amp current draw which indicates that the compressor is danged internally in a way that its piston(s) is(are) tight in the cylinder, a low-amp current draw, if below normal, may confirm internal wear on the compressor parts, and would support the diagnosis that the compressor is worn and inefficient. Where there are no gauge ports to actually measure compressor low side and high side vacuum and pressure, this simple electrical test is a useful first step.

  ~Abnormal air conditioner compressor pressure readings~

  Refrigerant line pressure readings which are abnormal (probably too low) on the high pressure side (compressor output) or on the low pressure side (compressor input or suction line) can indicate a problem with the compressor's ability to develop normal operating pressure ranges and thus will affect the cooling capacity of the air conditioning system. For more details on air conditioner refrigerant line pressures and how they are examined see COMPRESSOR PRESSURE READINGS

  ~Cooling Capacity of the Air Conditioning Duct System~

  Even if a very high BTUH capacity cooling system is installed, if the duct system is defective the ability of the system to deliver cool air to the occupied space can be severely or even totally lost. Duct System Efficiency (in percent) describes the percent of cooled air produced by the A/C equipment which is actually delivered to the occupied space. This number is less than 100% because of air flow restrictions and losses in the duct work. Duct Delivery Effectiveness is the percent of cooling capacity which is delivered through the registers into the occupied space. Registers themselves restrict air flow. See "DUCT SYSTEM DEFECTS" - see links at left.

  Cooling Capacity of the Whole Air Conditioning System

  So the ability of the entire A/C system to cool a building or rooms in it requires that both the cooling equipment and the duct system be in proper working order.

  These Simple Checks May Enable Inexpensive Repair of Lost Cooling Output from an Air Conditioner

  Before ordering an expensive air conditioner service call to restore lost cooling capacity, here are a few simple steps to perform. Some of these can be done by any homeowner, others may require a bit more expertise.

• Clogged filters can lead to lost cooling capacity first, because the clogged filter reduces the air flow through the system, meaning that you'll feel less air flow at the supply registers than was previously present.
• 
  
• Damaged cooling ducts such as ducts which have been improperly routed and are crimped, crushed, or have excessive bends can reduce cool air flow in an otherwise properly functioning system. One client had us drive a considerable distance to repair her apartment's central air conditioning system after having had several unsuccessful service calls. Apparently no one had managed to get into a rather tight and hard-to-enter attic crawl space where the cooling ducts were routed. We found that the main cooling duct had become disconnected. The attic was nice and cool but no cool air was being blown into the living area. Check the condition of the duct system for blocked ducts, loose leaky connections, closed dampers, crimps and bends, before calling your service technician.
• Cooling Coil Ice-Up A second result of the reduced air flow due to a dirty air conditioning filter can cause the evaporator coil (the cooling coil) in the air handler to become blocked by ice, stopping or significantly reducing cool air output from the system. A visual inspection of the cooling coil in the air handler can quickly show whether or not it's ice-covered. If the coil is iced-up and blocked, turn off the cooling system entirely until the ice has all evaporated and cleared. Be sure that your condensate drain is not blocked and that the water from melting ice will be properly disposed-of. If you replace all dirty filters on the system and remove ice from an iced coil and the coil ices up again when the system is turned back on, you may have the next condition in this list. For a detailed discussion of air conditioner or other refrigeration (or dehumidifier) cooling coil ice-up diagnosis and cure, see Air Conditioning Cooling Coil or Evaporator Coil Ice-up
• Improper refrigerant charge - too little: an air conditioner system which has lost some (but not most) of its refrigerant will sometimes run too cold at the evaporator coil, leading to coil icing and loss of cool air delivery in the home. If the filters are clean and the coil ices-up this condition may be present. A service technician will need to evaluate and test the system and if needed, adjust the refrigerant charge.
  Watch out for refrigerant leaks that lead to a repeat of this problem. If the system is low on refrigerant because it has a leak, it is much smarter to find and fix the leak than to simply keep adding refrigerant. If you keep adding refrigerant to a cooling system you're leaking possible contaminants into the environment as well as wasting money.
• Improper refrigerant charge - too much can also lead to improper air conditioning system operation and in some cases can damage the compressor. A service technician will need to evaluate and test the system and if needed, adjust the refrigerant charge. In this case the cooling coil is probably not going to ice-over, it just won't get cool.
• Loss of most refrigerant from an air conditioning system means that the cooling coil will not get cool at all. A service technician will need to evaluate and test the system and if needed, find and fix the refrigerant leak, evacuate the system, and install the proper refrigerant charge.
• Compressor problems such as an aging cooling compressor that is at or near the end of its life may be unable to properly compress the returning refrigerant gas to a sufficiently high pressure. A service technician will need to evaluate and test the system and if needed, replace the compressor. Since this is a costly repair, be sure to ask why the compressor failed and to correct any underlying cause (such as low voltage). Variations in line voltage can lead to improper compressor operation and loss of cooling output.