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.