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This article explains where to find and how to use the switches and controls for air conditioning and heat pump systems.

We include photographs to assist readers in recognizing cooling system defects. Other articles at this website discuss certain of these controls in greater detail. See SYSTEM OPERATION for a discussion of thermostats, zone dampers, and circuit breakers on air conditioners and heat pumps. Also see THERMOSTATS and THERMOSTATIC EXPANSION VALVES.

If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. see How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building. CONTACT us to add HVAC system switches or controls or diagnostic suggestions you do not find here.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

Air Conditioning & Heat Pump CONTROLS & SWITCHES

Detailed List of Air Conditioning & Heat Pump Parts, Switches and Controls

Here we list all of the controls and switches on a typical split system air conditioner with indoor and outdoor components include the items listed just below. If the A/C system won't operate, before requesting a service call check that it is turned on at every control, switch, or circuit breaker, and that the thermostat is properly set.

A/C - HEAT PUMP CONTROLS & SWITCHES
  Outside Switches, Fuses, Breakers
  Inside Switches,Components
  Air Handler / Blower Switches
  Blower Door Switches
  Backup Heat Controls
  CAPILLARY TUBES
  CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
  Compressor Condenser Switches, Controls
  Condensate Overflow Switch
  CONTACTOR RELAY DIAGNOSIS & REPAIR
  Duct System Switches
  Duct System Filters
  OPERATING CONTROLS, A/C & HEAT PUMP
  Starter Capacitors
  Thermostats & Controls
  Thermostatic Expansion Valves
  Motor Overload / Overheat Reset Switch
  Pressure Controls & Safety Switches
  Zone Damper Controls

The main operating controls for HVAC systems and their functions are are discussed at SYSTEM OPERATION where you will find a discussion of thermostats, zone dampers, and circuit breakers on air conditioners and heat pump systems.

We explain these many electrical switches and controls that control an air conditioner or heat pump system. You'll need to check these first if your air conditioner won't start or won't keep running. Other air conditioning and heat pump diagnostic procedures are at LOST COOLING CAPACITY.

If the A/C or heat pump system will not run check all of these control and safety switches listed here before calling your service technician. If someone or some condition has turned one of these switches off, resetting it may be all that's needed. Not all of these switches will be present on every system; fuses may be used instead of circuit breakers; fuse pullouts may be used instead of a circuit breaker or fuse at some service switches.

Watch out: Safety warning: do not put your fingers or hands inside of a heating furnace or air conditioner blower or blower compartment without making certain that all electrical power to the unit has been shut off. If the blower starts turning you can lose a finger, and there are also electrical shock hazards in these areas.

Key Air Conditioner or Heat Pump Main Electrical Control Switches, Fuses, or Circuit Breakers

• Air handler circuit breaker: in the electric panel there will be a switch controlling power to the air handler/blower circuit, perhaps two different circuits, one for the air handler unit, and a second for the compressor/condenser unit (the next item listed below) - also see CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
  
  
• A/C or Heat Pump Compressor circuit breaker: in the electric panel there will be a switch, circuit breaker or fuse controlling power to the outdoor compressor circuit - also see CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
  
  
• A/C indoor Air handler service switch: usually indoors at or right on the indoor air handler/blower unit, this switch is normally always "on" except during equipment servicing.
  
  
• A/C outdoor compressor/condenser unit service switch typically on the unit or on a building wall surface close to it. This switch is normally always "on" except during equipment servicing. Also see Outside Switches, Fuses, Breakers
  
  
• Air conditioner or heat pump thermostat: one or more indoor wall mounted thermostats must be set properly to call for cooling (or heating). Split system air conditioners and heat pumps may use a remote control device to turn the equipment on or off and to set the desired temperature. See THERMOSTATS.
  
  
• Other electrical switches and controls such as an air conditioner or heat pump pressure safety switch found on or near the compressor/condenser unit and in some window and through-wall units can also shut down an air conditioner or heat pump system, as we discuss below in this article.
  
  
• 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
• Air handler blower compartment safety switch: a safety interlock that will turn off electricity to the air handler or blower unit if the blower compartment door is not securely shut. If your air conditioner blower will not start this switch and the blower compartment doors should be checked. See BLOWER FAN OPERATION & TESTING
• Air conditioner/heat pump contactor relay switch: turns on high amp drawing equipment such as the compressor motor. See CONTACTOR RELAY DIAGNOSIS & REPAIR
• Air conditioner or heat pump pressure control & pressure safety switches: turns off the system at excessive refrigerant pressure and in some systems at too-low pressure. Also used in automotive air conditioning. See Pressure Controls & Safety Switches

List of Outside A/C or Heat Pump Service Switches, Fuses, Circuit Breakers

The pair of photographs just above show the outdoor air conditioner or heat pump compressor/condenser service control switch, in this case a circuit breaker, installed outside at a compressor for a ductless cooling system compressor. More photographs of a ductless or split system air conditioning system are at A/C TYPES, ENERGY SOURCES.

Our page top photograph is an important one to study further. The air conditioning system compressor/condenser service switch for this outdoor unit was a 240V fused circuit with outdoor fuses in the box shown in the photo. In this close up photograph you can just make out that someone has installed 1/2" copper pipes in place of the original fuses.

This might be a dangerous installation, risking fire as well as a burn up of the air conditioning equipment. But as Mark Cramer pointed out, if the circuit were properly protected by breakers or fuses at the main panel, the insertion of metal pipes in these fuse sockets just converts the device from a fuse box to a simple switch.

In any case, simply installing fuses would restore the proper safety device but it's likely that further testing and diagnosis of the electrical circuit and the compressor/condenser unit will be needed to determine why someone installed copper pipes where fuses belonged in the first place. When someone converts fuses to a switch in this location it may be because the air conditioning system was frequently blowing the fuses -- someone wanted to force the compressor/condenser to run.

Compressor Condenser Controls & Switches

Circuit breaker(s) at the electrical panel protect the circuit supplying power to the air conditioning system. Typically separate circuit breakers (or fuses) power the compressor/condenser unit and the indoor air handler/blower assembly.

Watch out: your HVAC equipment may be run out of a sub-panel rather than the main electrical panel. Be sure you have found all of the electrical panels, sub panels, and manual control switches for the equipment both inside the building and outdoors.

Watch out: really watch out: if you re-set a circuit breaker or replace a fuse and the breaker trips again or the fuse blows again, leave the equipment off and call a qualified service technician. You probably have an unsafe condition. Forcing electrical equipment to run can cause shock or fire.

Compressor/Condenser Unit: the "outside" portion of an air conditioner or heat pump, the compressor re-compresses refrigerant gas back into a liquid and in the process, moves heat (in the refrigerant) either from indoors to outside (air conditioning mode) or from outdoors to inside (heat pump mode) if the system is a heat pump. See COMPRESSOR CONDENSER for details of the diagnosis and repair of compressor problems.

Air Conditioner/Heat Pump Contactor Relay Switch

Air Conditioner, Heat Pump, Refrigeration System Operating Pressure Control Switches & Electrical Sensor Safety Switches

We distinguish between operating control pressure switches and safety switches that monitor against too-low or too-high refrigerant pressures in a refrigeration system. Both are described in detail at  Pressure Controls & Safety Switches. Excerpts are just below.

Operating Pressure Control Switches for Air Conditioners, Heat Pumps, Refrigeration Equipment

Operating pressure control switches set the normal compressor cut-in and cut out pressures in commercial refrigeration systems including air conditioners, coolers, refrigerators freezers. Commercial refrigeration equipment such as refrigerators (coolers) and freezers use a pressure control switch to set the cut-in and cut out pressures at which the compressor shall operate. The pressure control switch and the thermostatic expansion valve may both need to be inspected, tested, and set to cooperate with one another, as I describe in an old field service call report described at REFRIGERANT METERING DEVICES TEVs Shown at left is a Ranco™ single pressure control switch with an operating range of 12-50 psig and a differential range of 5-35 psig. Ranco produces a wide range of switches and controls including air conditioning controllers. This particular Ranco switch shown at left "opens" on low. Available from Grainger and other refrigeration equipment suppliers. The Ranco Type "O" single function pressure controls are very widely used on refrigeration systems and can operate either as normal operating controls or as protection devices (see Pressure Controls & Safety Switches).

Refrigeration System Pressure Safety Switches: protect against over pressure or under pressure in air conditioning or heat pumps

List of Inside Air Conditioner or Heat Pump Controls, Switches, Major Parts

Control Circuit Board - Air Conditioner / Heat Pump

Air Conditioner or Heat Pump Controls In or On the Air Handler Unit or Blower Compartment & At the Cooling Coil

Air Handler: the air conditioner or heat pump air handler is the "indoor" portion of the cooling (or heating) system whose job is to condition air from the living space by blowing air across a cooling coil (air conditioning) or heating coil (heat pump), sending the conditioned air on through supply ducts into the occupied space. The primary parts of the air handler unit include:

• Return air plenum: return ducts from the occupied space bring building air to this collection point for passage into the air handler
  
  
• Air filter: may be located in or near the return air plenum or preferably, at return air registers. Additional air filtration equipment may be installed at the air handler on the return-air side, such as electrostatic air cleaners, UV light sterilizers, HEPA filters, or other air quality improvement devices. See AIR FILTERS for HVAC SYSTEMS for details. Watch out: some HVAC systems may include a clogged or blocked air filter switch that you'll want to check. This may be simply an indicator that pops out to indicate that the filter has become too dirty and is blocking air flow.

A/C or Heat Pump Air Handler Blower Door Switches

• Blower compartment & blower fan: housing a fan, usually a round squirrel cage fan and electric motor (to operate the fan) which moves air from the return air plenum on towards the cooling or heating coil. An access door to the blower compartment should have a blower door interlock switch, a safety device which will prevent the blower from operating if the door is opened (see below). See FAN AUTO ON Thermostat Switch for details about what turns the blower fan on and off in normal use.
  
  
• Blower compartment door switch: an air handler blower compartment access door switch is present on newer units, and can be seen as a button or switch which is depressed when the blower compartment door or cover is properly in place. This switch shuts off the blower fan as a safety control if the door is opened. If your air conditioner won't run and someone has been fooling with it, be double sure that the blower compartment door is properly closed and that the interlock switch sensor button or lever is properly depressed to convey that fact to the system.
  
  
• Blower motor overload or overheat switch: a built-in overload protector used in some electric motors, especially the electric motor used to power the air handler's blower fan, may be tripped. see Blower Motor Switch for details.
  
  
• Cooling coil or heating coil (also called EVAPORATOR COIL or COOLING COIL) through which refrigerant is metered by a thermostatic expansion valve (see below) in order to cool and dehumidify (or in the case of heat pump mode, warm) air from the occupied space as air is blown across this coil.
  

Backup Heat Controls on Heat Pumps

• Heat Pump Heat & Backup Heat Controls: if your cooling is provided by a heat pump system, during the heating season the same equipment is used to provide heating as was used to provide cooling during hot weather. Heat pumps in climates where temperatures can get lower than the heat pump can handle include a backup heat source and all heat pumps include additional controls: an outdoor thermostat that monitors outside temperature and decides when to switch the backup heating system on; a reversing valve that switches the direction of refrigerant, and an indoor thermostat which can be set to auto, heat, cool, or off modes.
  
  
• Supply plenum: a compartment which receives conditioned air from the cooling (or heating) coil and delivers this air to one or more ductwork systems which in turn move air to various areas of the occupied space.
  
  See AIR HANDLER / BLOWER UNITS for details.

Condensate Overflow Pan Safety Switch

Condensate overflow tray sensor switch: at the air handler, especially in an attic or closet or upper floor air handler, installers may provide an electrical switch (rather than a separate drain pipe) to detect spillage of air conditioner condensate out of its normal air conditioning condensate drain pipe. When we cool air inside the air handler, that step causes moisture in the air to condense out as a liquid condensate that must be collected and disposed-of. The condensate overflow switch is a sensor which turns off the air conditioning system as soon as it detects water in the condensate drip tray - thus avoiding a costly leak into building ceilings or floors and perhaps avoiding a mold contamination problem. See DRIP TRAY DEFECTS and Float Switch on Condensate Tray. Thanks to Lester Richter for this tip.

Circuit breaker - compressor: in the building main electric panel there will be a switch controlling power to the compressor/condenser unit. Typically this is a 240V circuit operated by a double pole circuit breaker or a fuse pair.

Circuit breaker - air handler/blower: in the electric panel there will be a circuit breaker or fuse controlling power to the air handler/fan unit which distributes cool air in the building. This will typically be a separate 120V circuit dedicated to protecting the circuit which supplies electric power to this equipment

Duct System Components, Controls, Switches

Duct System: the air conditioning air ducts (or ductwork) (or heat pump duct work) carry conditioned air from the air handler to various rooms in the occupied spaces of the building.

Return air ducts bring air from the occupied space to the air handler. In some installations only a single return air register and return air duct may be installed, usually in the ceiling over a stairwell in a two-story home; where multiple return ducts are provided you will find two or more return registers in the building; If you observe that most rooms have only a supply register and duct and no individual return air ducts, keeping the room doors open will probably improve air circulation and reduce heating or cooling costs for the building.

Supply air ducts bring air from the air handler (where it has been cooled and dehumidified, or heated if a heat pump is in heating mode) back into the occupied spaces in the building. Where each supply duct enters a room through the room ceiling, wall, or floor, a finned supply register should be installed to permit control of the direction and amount of air that exits the duct at that location.

Zone dampers: HVAC ducts in some installations may include motorized zone dampers controlled by individual room thermostats or switches.

See ZONE DAMPER CONTROLS for details about these controls.

See DUCT SYSTEMS for details about inspecting, diagnosing, and correcting a broad range of HVAC air duct problems.

Duct System Filters on HVAC Systems

Starter Capacitors and Start/Run Capacitors on HVAC System Motors

A bad starter capacitor or the need for one where none is installed can be the cause of motors that fail to start, motors that chatter or stutter, or electric motors that won't keep running (bad run capacitor). See CAPACITORS for HARD STARTING MOTORS.

Thermostats & Controls on HVAC Systems

An air conditioning system thermostat is a switch to turn on or off the A/C equipment as indoor air temperature varies around the thermostat's set point.

The left hand photograph above shows a typical indoor thermostat used to control heating or cooling. Note that in this photo the thermostat is switched to "heat" mode. The air conditioner will not run with the switch set to "heating". The right hand photo shows a remote control thermostat used indoors to control the indoor wall-mounted cooling unit of a ductless cooling system.

See THERMOSTATS for details of the operation of air conditioning, heat pump, and heating system thermostats and switches.

More photographs of a ductless air conditioning system are at A/C TYPES, ENERGY SOURCES.

Thermostatic Expansion Valves at A/C or Heat Pump Coils

Another type of thermostat that controls heating and cooling in your HVAC or heat pump system is the TEV or thermostatic expansion valve. This device monitors temperatures at the evaporator coil in the air handler and meters refrigerant into the coil accordingly. TEV devices can fail in several ways, Often involving a clogged sensor tube.

While it's possible to fool around with some TEV's, tap on them, adjust their metering rate, etc. this task should be left to your service technician since without proper training and test equipment you will have little idea where the adjustment has been set (if it can be set).

Motors in HVAC Systems: Electric Motor Overload or Overheat Reset Switches

There are at least three electric motors in a conventional air conditioning or heat pump system, plus sometimes a fourth:

1. An indoor blower fan motor - causing air to move across the evaporator (cooling) coil [or heating coil in heat pump mode], and through the duct work into occupied spaces.
2. An outdoor compressor motor - compressing refrigerant gas back into a liquid
3. An outdoor compressor unit fan motor - draws air across the condensing coils to condense hot refrigerant gas back to liquid form.
4. Condensate pump motor: me systems also use a condensate pump or condensate drain pump to help remove condensate from the air handler to a building drain. A failure here that leads to lost cooling can be subtle: if the condensate removal system fails (bad pump, clogged drain) and if condensate spills into an overflow pan that uses a sensor switch to detect this condition, the failed condensate motor can actually stop an air conditioner from running.

Any of these motors can fail to start or may be "off on reset" due to a motor overload, or motor overheating.

Zone Dampers & Zone Controls on Heating and Air Conditioning Systems

Some heating and air conditioning systems use manual or automatic zone dampers to control the flow of conditioned air to different building areas. A manual damper is just a lever somewhere in the duct work that opens or closes a baffle inside the duct to limit air flow through that duct section.

An automatic zone damper may be controlled by an individual thermostat for the area served by that zone. So if the heating or cooling system is not running, or if it is running but not sending air to an area in the building, look for and check out any manual and automatic zone damper controls.

Details about zone dampers used on ductwork: warm air zones and air conditioning zones and zone dampers are at ZONE DAMPER CONTROLS.

If the A/C system will not run check all of these control and safety switches before calling your service technician. If someone has turned one of these switches off, resetting it may be all that's needed. Not all of these switches will be present on every system; fuses may be used instead of circuit breakers; fuse pullouts may be used instead of a circuit breaker or fuse at some service switches.

Watch out: Safety warning: do not put your fingers or hands inside of a heating furnace or air conditioner blower or blower compartment without making certain that all electrical power to the unit has been shut off. If the blower starts turning you can lose a finger, and there are also electrical shock hazards in these areas.

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Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

AIR CONDITIONING & HEAT PUMP SYSTEMS

A/C - HEAT PUMP CONTROLS & SWITCHES
  Outside Switches, Fuses, Breakers
  Inside Switches,Components
  Air Handler / Blower Switches
  Blower Door Switches
  Backup Heat Controls
  CAPILLARY TUBES
  CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
  Compressor Condenser Switches, Controls
  Condensate Overflow Switch
  CONTACTOR RELAY DIAGNOSIS & REPAIR
  CONTROL CIRCUIT BOARD, A/C
  FAN, COMPRESSOR/CONDENSER UNIT
  Duct System Switches
  Duct System Filters
  OPERATING CONTROLS, A/C & HEAT PUMP
  Starter Capacitors
  Thermostats & Controls
  Thermostatic Expansion Valves
  Motor Overload / Overheat Reset Switch
  Pressure Controls & Safety Switches
  Zone Damper Controls

A/C DATA TAGS

AIR CONDITIONER NOT WORKING

BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING

CAPACITORS for HARD STARTING MOTORS
CAPILLARY TUBES

CIRCUIT BREAKER SIZE for A/C or HEAT PUMP

A/C - HEAT PUMP CONTROLS & SWITCHES
COOL OFF HEAT Thermostat Switch

DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP

ELECTRIC MOTOR OVERLOAD RESET SWITCH

EXPANSION VALVES, REFRIGERANT

FAN AUTO ON Thermostat Switch

FAN LIMIT SWITCH

MOTOR OVERLOAD RESET SWITCH

SYSTEM OPERATION
  OPERATING CONTROLS
  SAFETY CONTROLS

THERMOSTATS, HEATING / COOLING
  Types of Building & Room Thermostats
  How Thermostats Work
  Detailed Guide to Room Thermostats
  How to Set the Thermostat
  COOL OFF HEAT Thermostat Switch
  FAN ON AUTO Thermostat Switch
  HEAT ANTICIPATOR Adjustment
  HEAT ANTICIPATOR Mini Ammeter to Check
  HEAT PUMP Thermostats - Outdoors
  INSTALL & WIRE Thermostats
  TEMPERATURE RESPONSE of Room Thermostats
  SWITCH FUNCTIONS on a Room Thermostat

THERMOSTATIC EXPANSION VALVES

WATER COOLED AIR CONDITIONERS

• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Thanks to Lester Richer, a professional home inspector, for the reminder that a bad air conditioner condensate drip tray switch can shut the whole system down.
• Behr Hella Service A/C pressure switches,
• Grainger, http://www.grainger.com/
• Ranco Corporation, http://www.invensyscontrolseurope.com/ranco/ Tel (Europe) +44 (0)845 130 5522
• Sensata Technologies, 529 Pleasant Street, B41 Attleboro, MA 02703-2964 Phone: 1-248-692-5600 Fax: 1-248-692-5630 Email: auto-mktg@sensata.com Web: www.sensata.com, pressure switches for automotive air conditioning systems
• Micro Pneumatic Logic, Inc., Pompano Beach, Florida Tel. (954) 973-6166 - pressure switches

How to diagnose and fix an air conditioning system that is not working

Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.

If your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.

CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.

OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume

LOST COOLING CAPACITY: what to do when not enough cool air comes out of the system

What to check first if there is no cool air or not enough cool air

Compressor failure diagnosis: basic checks of the air conditioner compressor

Ducts & Air Handler diagnosis: basic checks of the indoor air handler (blower), air ducts, and filter systems

COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units

AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself

DUCT SYSTEM DEFECTS: problems with the air duct system, air filters, supply registers, return air registers

A/C REFRIGERANT LEAK DETECTION: how to use a TIF5000 to detect air conditioning refrigerant gas leak

A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair - a detailed air conditioning system diagnostic checklist

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

Complete List of Air Conditioning & Heat Pump Design, Inspection, Repair Books at the InspectAPedia Bookstore.

Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982

Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979

"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]

Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).

Air Conditioning Inspection, Diagnosis, Repair, Efficiency all the basics for home owners, inspectors, new repairmen

Air Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard

Asbestos HVAC Ducts and Flues field identification photos and guide

Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation

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