Air Conditioning & Heat Pump System Components Guide
AIR CONDITIONER COMPONENT PARTS - CONTENTS: What are the indoor and outdoor components of an air conditioning or heat pump system?. What does each air conditioner or heat pump component do? Photographs of air conditioning & heat pump components. Sketches / drawings of air conditioner & heat pump components
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
HVAC heating, ventilation, air conditioning & refrigeration system component identification guide:
This article lists and explains the function of the basic components of an air conditioning or heat pump systems and provides detailed inspection, diagnostic, and repair advice. We include photographs to assist readers inrecognizing cooling system defects.
Below we begin a more detailed A/C system inspection list of air conditioning system components. If your air conditioning system is not working properly, see REPAIR GUIDE for AIR CONDITIONERS
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 or Heat Pump System
AIR HANDLER / BLOWER UNITS (AHU) (shown at left above and in the Carson Dunlop sketch below) 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 (evaporator 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 or COOLING COIL (also called the "cooling coil" is connected to high pressure and low pressure (suction) refrigerant lines.
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
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).
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"
Central air returns are most common on air conditioning retrofit installations (adding A/C to an existing building). Sketch courtesy of Carson Dunlop [Click to enlarge any image]
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.
List & Photos of Outdoor Air Conditioning & Heat Pump System Components
Above we show two typical compressor/condenser units outdoors. The main internal components of the compressor/condenser unit are listed below:
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. Sketch courtesy of Carson Dunlop Associates.
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.
Condensing coil receives high pressure refrigerant gas from the compressor and cools this refrigerant gas back to a liquid state.
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.
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.
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
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.
Thanks for the nice comment Anon. We will always also welcome your questions, comments, critique - which helps us both.
Question: I have been cautioned to stay clear of variable-speed blower options
(Mar 14, 2014) Phil said:
I'm in the market for a replacement electric/gas pack unit. I have been cautioned to stay clear of variable-speed blower options and their sophisticated electronic controls for lack of durability. The reason given was sensitivity to power fluctuations - drop-outs and surges. Likewise, that copper/aluminum fin condenser coils of today are more leak prone than their all-aluminum cousins. Do you agree and if so could you recommend some 13-seer models for their use of more durable/reliable components? Or, help me know what to look for? Thanks for your expertise and help cutting through the marketing confusion!
Thanks for the "expertise" compliment Phil but with a little embarrassment, this question is beyond our expertise. While your surmise sounds sensible, in fact across thousands of readers and comments, I have not seen a particular pattern indicating that variable speed blowers fail more frequently than their simpler single speed units. Indeed for systems providing both heating and cooling we generally want a blower capable of operating at at least two different speeds for the two different modes.
I suspect that power fluctuations are more of a worry for controlling circuit boards in general.
Back in 2009, in "Comparing Motor Technologies", achrnews.com Brian Michael reported that constant torque motors, a comparatively new design in use in HVAC systems (dating from a Regal-Beloit (General Electric) design in 2006) offered high efficiency that helps meet the 13-SEER HVAC models in your question. That article does not cite the concerns you raise.
Question: what is meant by "high side" and "low side" on an air conditioner or heat pump system?
(July 23, 2014) Anonymous said:
sometimes they say high side and low side is this referring to high pressure and low pressure?
High side pressure is on the compressor outlet side and low side pressure is on the compressor suction side. On the outlet side of the AC or heat pump compressor the refrigerant is at high pressure (over 100 psi) while on the suction side the refrigerant pressures are quite low.
(Aug 28, 2014) donrebich said:
Question: We began having a problem with the unit blowing hot air and going outside to the unit finding the fan not working but after hitting a red button the unit came on and functioned properly. Calling a service co and detailing what had transpired he claimed it was the fan motor. Another tech came out and claimed the system had excess frion, the high pressure side was at 280 and suction was 75 on the compressor. Being extreamly hot outside, perhaps causing either the fan motor to kick the system off or a pressure swithch.
Question: can you repair a defective air conditioner compressor?
(Mar 4, 2015) Rick Regaspi said:
May I ask if the defective compressor motor of Air-con can be repaired? or is there any repair shop for compressor motor?
Rick: residential HVAC compressor motors are typically a sealed unit that cannot be field-repaired.
Question: split system is not cooling and not dehumidfying well and it squeals
(May 3, 2015) Robert said:
My split system is not dehumidifying the air and is not cooling very well. There is also a squealing sound when the unit turns on and a lot of noise in the cabinet where the A-coils are when the unit is turned off.
The copper line that is not insulated is cold rather than warm like it usually is.
Could there be a leak or might the A-coils need to be cleaned?
I would investigate the squealing first - look for a failing blower assembly, belt, or in a split system, more likely a motor.
Ask a Question or Search InspectApedia
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Thanks to Scott at SJM Inspect for suggesting this EPA document and for technical editing remarks regarding our air conditioning website,
SJM Inspection Service LLC, serves the entire state of CT, sjminspect.com 203-543-0447 or 203-877-4774
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones