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This page provides an index to key articles describing air conditioner & heat pump inspection, installation, troubleshooting & repair procedures, parts, manuals & codes for all types of residential and light commercial central air conditioning and heat pump systems.
Page top image & air conditioning schematic drawing below were provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Air Conditioner / Heat Pump Installation, Troubleshooting, Repair
An air conditioner can fail in a number of ways:
unit won't turn on
loss of air conditioner cooling capacity
reduced air conditioning output temperatures
loss of cool air supply
loss of air flow entirely
These failures can be due to a variety of problems with one or more components of an air conditioner or
air conditioning system.
Just below we give brief descriptions of the main types of trouble you may encounter with an air conditioner or heat pump. Start by reviewing those problem areas.
For air conditioner or heat pump troubleshooting that can be done by many building owners or occupants, see our separate article
Air Flow Problems in Air Conditioning or Heat Pump Systems
Weak or no air flow coming out of the supply registers in each room. Often the problem is as simple as a dirty air filter or dirty indoor blower fan in the air conditioner or heat pump air handler unit.
Cooling Problems in an Air Conditioner or Heat Pump
If there is good air flow out of supply registers but in cooling mode the air does not get cool, or in heating mode (for heat pumps) the air delivered does not get warm the trouble could be that the outdoor compressor unit is not working or that the system has lost its refrigerant charge.
Many service calls for non-working air conditioners or heat pumps turn up an electrical problem.
The most basic electrical problem is that a motor or HVAC unit simply won't start. Other electrical problems include buzzing noises at relays or burning electrical smells.
But first remember to check the system power switches at the air handler indoors, at the compressor/condenser outdoors, and in the electrical panel.
If your A/C system is just not working at all, be sure to check all of our electrical and control setting suggestions first.
Indoor Air Handler / Blower Problems on HVAC systems
Besides weak air flow that we mentioned above, more serious problems such as a failing blower motor or no a blower fan that never starts at all can prevent the delivery of cooled or heated air.
We see a number of problems with fans and fan motors in both the compressor/condenser unit and in the air handler/blower fan unit. Some of those fan problems are mechanical - like a loose fan belt or blade.
A more simple mechanical problem is an air supply or return duct that has become disconnected, loose, crushed, or leaky, leading to the failure of the A/C or heat pump system to deliver air to supply registers. We class these as duct system problems.
Outdoor Compressor/Condenser Unit Problems on Air Conditioners or Heat Pumps
The unit has at least two motors: the sealed compressor motor that compresses refrigerant gas so that it can be condensed back to liquid form, and a fan motor that spins the fan necessary to move outdoor air across the condenser unit coils.
An outdoor compressor/condenser unit may refuse to start, may be noisy, or may fail to do its job to compress the system's refrigerant from a gas back to liquid form.
Control relays, boards, switches in the condenser unit may fail, or a refrigerant leak at the unit can cause loss of cooling or heating even though the indoor blower unit delivers air at the supply registers.
AIR CONDITIONER TEMPERATURES - what are the normal input and output temperatures and air temperatures & where are the measured?
AIR HANDLER / BLOWER UNITS - home - problems with the air handler, air filters, and the cooling coil itself
BACKUP HEAT for HEAT PUMPS - types of backup heat, diagnosing back up heat pump heat not working properly, types of backup heat; problems with backup heat; begin here if your heat pump is not providing enough heat or if your air conditioning system provides heat when it should be providing cooling
BLOWER LEAKS, RUST & MOLD - damage that can prevent the blower from working or may be blowing contaminants into the occupied rooms
COMPRESSOR / CONDENSER REPAIR - home - problems with air conditioner compressor/condenser units - use this link to find our full list of HVAC condenser/compressor diagnostic & repair articles.
CONDENSATE HANDLING, HVAC - home - cooling air produces condensate that must be disposed-of properly
CONTROLS & SWITCHES on A/C or HEAT PUMP - 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 and some refrigeration class instructions opine that 80% of problems on these systems are electrical in nature. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
Controls and switches on air conditioners and heat pumps also include:
DEHUMIDIFICATION PROBLEMS - air conditioner cools but does not dehumidify - indoor humidity remains too high
ELECTRIC MOTOR DIAGNOSTIC GUIDE - diagnostic procedures for electric motors used on oil burners, air handler blower assemblies and fans, air conditioners, heat pumps, well pumps, etc.
LOST COOLING CAPACITY - what to do when not enough cool air comes out of the system - use this link to see our key diagnostic articles if your A/C unit is not cooling or the air flow is too weak.
MANUALS & PARTS GUIDES - HVAC - where to find air conditioner, heat pump, and heating repair manuals, owners guides, installation guides, and parts lists
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 volumes
REFRIGERANT LEAK DETECTION - how to find and fix air conditioning refrigerant gas leaks. This page includes our diagnosis and repair articles for refrigerant leaks.
REVERSING VALVE on HEAT PUMPS - when this control fails the system may work only in heating mode, or only in cooling mode, but not both
On 2023-05-30 by Ben
- new cooling coil doesn't fit my existing indoor air handler
I need to replace my A/C on the outside of my house and the evaporator coil. My problem is that my existing furnace has a 13in wide evaporator coil and I can't find that size anywhere. The smallest I can find are 14 and 14.5 inch. Can I use a bigger evaporator coil on my furnace? What would be need to do so? Thank you!
On 2023-05-30 by InspectApedia Publisher (mod) - Upflow furnace installation of an add-on cooling coil or evaporator coil
@Ben,
Yes you can use a larger evaporator coil, but be sure to discuss with the installer just how the air plenum should be shaped for best air flow across the coil.
Watch out: if your new coil is too large for the system's design it may cool the building without adequate dehumidification (because it cools everything down too fast to complete moisture removal).
The transition plenum that you install will be shaped to direct air flow across the coil without creating dead air spaces.
Don't just slap on a larger coil atop the air handler, sticking out at the sides.
Here is an often-quoted excerpt from Trane's IO manual
FURNACE
UPFLOW INSTALLATION
Standoffs and screws (See Figure 1, page 6) are included with the cased coils for attachment to the furnace. NOTE: The top flanges on the furnace must be bent 90 degrees upward to allow the coil attachment.
There are clearance alignment holes near the bottom of the coil wrapper. Drill screws are used to engage the furnace top flanges. The standoff is inserted into the cabinet alignment hole.
The drill screws are inserted through the standoffs then screwed into the furnace flange. The coil is always placed downstream of the furnace airflow. The above instructions apply only if the coil is on top of an upflow furnace.
COIL
a. Apply gasket material (duct seal field supplied) to ALL mating surfaces between the furnace and the coil case.
b. Set the coil case on top of the furnace. Connect the ductwork to the coil case using the field supplied screws.
c. Secure the coil case to the furnace and seal for air leaks as required.
Question: how do I figure out the replacement for my old AC Compressor Capacitor
Retail Stephen
Wondering if anyone can figure out the replacement for my old ac capacitor. The newer says HCF (Herm, common" Fan) but based on the wiring diagram it shows BCA. Please help!! Please see pictures attached - 2022/08/18
Moderator reply:
Sure - the values are right on the cap, but you can also follow the steps at
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In addition to any citations in the article above, a full list is available on request.
[1] "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]
[2] Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects" section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and home inspection educator.
[3] Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
[4] 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 5/16/07
[5] Thanks to Joe Panimondo for technical editing, April 2011
[7] HVAC brands discussed include but are not limited to: Lennox, American Standard, Amana, Everrest, Goodman, Frigidaire, Coleman and Gibson. Brands of related air handling equipment include Honeywell, Aprilaire, White-Rogers, Broan. Nutone, Fantech, Venmar, Arzel, Hi-Velocity, Vanguard, Wirsbo, Weil McLain, Unico, Heat Link, A.O. Smith, Water Furnace, ClimateMaster, Geo-Excel, Command Aire, Friedrich, LG, Mitsubishi, Sanyo, Hart &
Cooley, Munchkin, Superstor Ultra, Lochinvar and Knight HVAC equipment.
[8] Bureau of Labor Statistics, U.S. Department of Labor, Occupational Outlook Handbook, Heating, Air Conditioning, and Refrigeration Mechanics and Installers,
at https://www.bls.gov/ooh/installation-maintenance-and-repair/heating-air-conditioning-and-refrigeration-mechanics-and-installers.htm (visited June 15, 2022).
[8a] Bureau of Labor Statistics, U.S. Department of Labor, Occupational Outlook Handbook, 2014-15 Edition, Heating, Air Conditioning, and Refrigeration Mechanics and Installers, on the Internet at http://www.bls.gov/ooh/installation-maintenance-and-repair/heating-air-conditioning-and-refrigeration-mechanics-and-installers.htm (visited February 05, 2014).
[9] HVAC Education, Training Accreditation agencies: Quoting the U.S. DOL HVAC website above: After completing the programs below, new technicians generally need between 6 months to 2 years of field experience before they are considered proficient. Three accrediting agencies have set academic standards for HVACR programs:
HVAC Excellence is a not for profit organization that has been serving the HVACR industry since 1994. It is our goal to improve competency through validation of the technical education process. By setting standards and verifying that they have been met, we inspire the industry to excel.
We know that all of the challenges that face our industry are achievable by continuous improvement in the way that we prepare technicians.
[11] National Center for Construction Education and Research, 3600 NW 43rd Street, Bldg. G, Gainesville, FL 32606, Tel: 888.622.3720, Web: http://www.nccer.org/
Quoting: NCCER is a not-for-profit education foundation created to develop industry-driven standardized craft training programs with portable credentials and help address the critical workforce shortage facing the construction industry.
[12] The Partnership for Air-Conditioning, Heating, and Refrigeration Accreditation, (PAHRA), 2111 Wilson Blvd., Suite 500, Arlington, VA 22201-3001, USA, Tel: (703) 524-8800, Web: http://www.pahrahvacr.org/
Quoting: The Partnership for Air-Conditioning, Heating, Refrigeration Accreditation (PAHRA) is an independent, third party organization that is a partnership between heating, ventilation, air-conditioning and refrigeration (HVACR) educators and the HVACR industry that will award accreditation to programs that have met and/or exceeded industry validated standards. This programmatic accreditation program is the only one that is supported by the major industry associations.
[13] HVAC Training Courses, Schools: HVAC Technician Training Schools [http://technicianschool.net/hvac-technician-training-schools/], lists the following schools offering technical courses may offer specific training programs for potential careers, including HVAC technicians. Among HVAC schools that website lists are
Everest Colleges [http://www.everest.edu],
Florida Career College 7891 Pines Blvd Hollywood, FL 33024 http:// www.careercollege.edu/,
Lincoln Institute 2299 Vauxhall Road Union, NJ 07083 http:// www.lincolnedu.com/
NOTE: when considering an HVAC training course or school, check the HVAC education accrediting associations listed above.
[14] Ratib Bakera is member of Refrigeration Service Engineers Society (RSES), an International training organization for the HVACR industry provides educational and certification programs to HVACR professionals of all experience levels. Web: www.rses.org , provides information on the organization and its training materials. Independent testing and certification of HVAC technicians is provided by North American Technician Excellence - NATE - see www.natex.org.
NATE is supported by ASHRAE, the US EPA, and a host of other trade and professional associations.
[15] Singer brand HVAC equipment brand history: Singer was bought by & became the climate control unit of Dallas-based Snyder General Corp. (founded by a former Singer HVAC manager) in 1982. The name Singer was dropped in 1984. In 1984 Snyder General operations included Arcoaire, Comfortmaker, and McQuay. In 1991 Snyder General sold Arcoaire & Comfortmaker to Inter-City Products. In 1994 Snyder General was acquired by Hong Leong Group Malaysia. Snyder General is at 2001 Ross Avenue Dallas, TX 75201.
[16] Lennox air conditioning and heat pump owners manuals for air conditioners, air handlers, furnaces, heat pumps, indoor air quality systems, packaged units, water heaters, zone controls and other controls such as thermostats, are provided by Lennox at http://www.lennox.com/support/manuals.asp
[23] Air Diffusion Council, 1901 N. Roselle Road, Suite 800, Schaumburg, Illinois 60195, Tel: (847) 706-6750, Fax: (847) 706-6751 - Email: info@flexibleduct.org - www.flexibleduct.org/ -
"The ADC has produced the 4th Edition of the Flexible Duct Performance & Installation Standards (a 28-page manual) for use and reference by designers, architects, engineers, contractors, installers and users for evaluating, selecting, specifying and properly installing flexible duct in heating and air conditioning systems.
Features covered in depth include: descriptions of typical styles, characteristics and requirements, testing, listing, reporting, certifying, packaging and product marking.
Guidelines for proper installation are treated and illustrated in depth, featuring connections, splices and proper support methods for flexible duct.
A single and uniform method of making end connections and splices is graphically presented for both non-metallic and metallic with plain ends."
The printed manual is available in English only. Downloadable PDF is available in English and Spanish.
[24] Engineering toolbox properties of water - http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html and email: editor.engineeringtoolbox@gmail.com web search 09/16/2010
[25] Owens Corning Duct Solutions - www.owenscorning.com/ductsolutions/ - provides current HVAC ductwork and duct insulating product descriptions and a dealer locator. Owens Corning Insulating Systems, LLC, One Owens Corning Parkway, Toledo, OH 43659 1-800-GET-PINK™
[26] "Flexible Duct Media Fiberglas™ Insulation, Product Data Sheet", Owens Corning - see owenscorning.com/quietzone/pdfs/QZFlexible_DataSheet.pdf "Owens Corning Flexible Duct Media Insulation is a lightweight, flexible, resilient thermal and acoustical insulation made of inorganic glass fibers bonded with a thermosetting resin."
[30] Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' TECHNICAL GUIDE to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
[32] FlowKinetics LLC, 528 Helena Street Bryan, Texas 77801 USA, Tel: (979) 680-0659, Email: inform@flowkinetics.com, Website: www.flowkinetics.com, "FKS 1DP-PBM Multi-Function Meter Pressure, Velocity & Flow User’s Manual", web search 07/16/2012, original source: http://www.flowkinetics.com/FKS_1DP_PBM_Manual.pdf [copy on file] and "FKT Series Flow Measurement And Pressure Acquisition System User's Manual" http://www.flowkinetics.com/FKTSeriesManual.pdf [copy on file]
[33] Histoire de l'Académie royale des sciences avec les mémoires de mathématique et de physique tirés des registres de cette Académie: 363–376. Retrieved 2009-06-19.- Pitot Tubes, Henri Pitot (1732)
[34] Wikipedia Web: https://www.wikipedia.org/ provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative.
"Pressure sensor", retrieved 7/16/2012
[35] "GE Zoneline® Owners Manual and Installation Instructions, Heat/Cool Model 2900, Heat Pump Model 3900", General Electric Corporation, [copy on file].
[36] "GE Zoneline® Owners Manual and Installation Instructions, Heat Pump Model 5800", General Electric Corporation, [copy on file].
[38] N Lu, YL Xie, Z Huang, "Air Conditioner Compressor Performance Model", U.S. Department of Energy, August 2008, [copy on file as PNNL-17796.pdf] Available to the public from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Rd., Springfield, VA 22161 ph: (800) 553-6847, fax: (703) 605-6900 email: orders@ntis.fedworld.gov online ordering: http://www.ntis.gov/ordering.htm
[39] Yinger R, R Bravo, and D Martinez. 2006 Air Conditioner Stalling Effects Study/Air Conditioner Testing Procedures. Southern California Edison, Rosemead, California
[40] Bravo, R, R Yinger, and L Gaillac. 2006. Conditioner Stalling Unit Level Solutions Test Report. Southern California Edison, Rosemead, California.
[41] Lu N, B Yang and Z Huang. 2008a. Evaluation of Southern California Edison Air-Conditioner Stalling Solutions. PNNL-17686, Pacific Northwest National Laboratory, Richland, Washington.
[42] Danny S. Parker, John R. Sherwin, Bart Hibbs, "Development of High Efficiency Air Conditioner Condenser Fans", ASHRAE Transactions June 2005, [copy on file as FSEC-CR-1674-05.pdf]
[43] Thanks to Alexis Claro alexis.hvaced@gmail.com who maintains a website offering information about HVAC training found at hvaced.com/hvac-training .
Singer brand HVAC equipment brand history: >Singer was bought by & became the climate control unit of Dallas-based Snyder General Corp. (founded by a former Singer HVAC manager) in 1982. The name Singer was dropped in 1984. In 1984 Snyder General operations included Arcoaire, Comfortmaker, and McQuay. In 1991 Snyder General sold Arcoaire & Comfortmaker to Inter-City Products. In 1994 Snyder General was acquired by Hong Leong Group Malaysia. Snyder General is at 2001 Ross Avenue Dallas, TX 75201 .
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In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.