~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 ... .