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Frequently Asked Questions (and answers) about air conditioners & heat pumps
FAQs about air conditioning and heat pump systems help diagnose inspection, installation, troubleshooting or repair problems.
These FAQs are part of an article series discussing how to inspect and repair all types of residential air conditioning systems (A/C systems). Page top image provided courtesy Carson Dunlop Associates.
(Mar 16, 2016) james said:
is an air conditioning refrigerant liquid or a gas? are there any concerns with a leakage of a window ac unit?
James in a refrigeration system the refrigerant changes states: on the "low pressure" side of the cooling coil it is in a gas; on the high pressure side of the system after exiting from the condensing coil, the refrigerant is a liquid.
Leaks of refrigrant at any AC unit will mean it will stop working; and you're contaminating the environment.
Question: overcharged for air conditioner repair that replaced just a capacitor?
(Apr 12, 2016) LHS said:
I had an encounter and would like to share this.
My air compressor stops working.
I called for a repair. The repaired took less than 5 minutes and change a capacitor. The parts cost is $30 and the overall sum adds up to $120. The huge gap was in questions and ask for justification. Unwillingly the man reduced to $80.
So please beware of such incidents and always see for the work that is being done. Those dishonest repair that we as a consumer should learn how to protect ourselves.
Reply: there is a danger of paying too much but also a danger in paying too little
Indeed most trades people have a minimum charge for a service call, and to a homeowner who finds that the call took just five minutes, the cost of that (CAPACITORS for HARD STARTING MOTORS) repair can be upsetting.
Please consider, however, a different point of view about the true cost and fair charge for HVACR repairs:
The $80 that you paid was not simply for "5 minutes of work and a $30. part" or a net of $50. for the 5 minutes of work. That $50. covered also the following:
1. The knowledge and expertise on the repair person's part that allowed her or him to quickly determine what was wrong, and to make the repair properly, effectively, and without causing some other problem.
That expertise comes from many hours of classroom training and probably years of job experience. Knowledge and expertise have tremendous value, and also a big investment of time and effort on the part of the repair person to develop that expertise.
2. Lesser, but also important, you were paying for someone to
2.a. take the time to drive to and from your home - that's essentially unpaid, unproductive time
2.b. drive a heavy truck (not cheap to operate) that carries a spare parts inventory (a large tie-up of money in inventory that has to be monitored, maintained, replenished) that included exactly the part that was needed
3. Pay a small contribution to health care, retirement pension, truck insurance, liability insurance, warrantying the work performed, and other fundamental but essential components of what it costs to hire and train a service technician and send him or her into the field.
You're not just paying for the part and 5 minutes of someone's time you're paying for the value of that expertise, having parts on hand, and bringing the right parts and right repair to your home.
There's an old surgeons joke about that sort of fee when the patient complained that the surgeons' bill of $4,500. to remove a small tumor was too high as the operation only took 14 minutes. The surgeon replied: OK I'll re-write the bill:
Charge for 14 minutes of time (at my hourly rate) = $75.00
Charge for your share of 18 years of schooling, 21 years of surgical experience, and a portion of my costs for the operating room, anesthesiologist, nursing staff, equipment, medicine, bandages, and liability insurance: $4,425.
See HOW MUCH SHOULD YOU PAY what is the right amount to pay for a professional building inspection or for environmental tests of a building? Environmental Testing Fees. Home Inspection Fees. It is a mistake to pay too much for a professional service. It may be a bigger mistake to pay to little for a professional service.
(Apr 14, 2016) ronaz said:
agree with (mod) comments - OK to pay for expertise but how about the following which happened to me last week:
Called reliable (?) a/c company for $79 tuneup,tech says large capacitor out, compressor won,t start, $437 to replace (Mars 11069 - $32 on Amazon), told him no way,
he called office who dropped price to $295- I declined & told him to return unit to original condition by replacing fuse, Miracle of miracles, fan & compressor turn on. Kicker::: Impossible to get capacitor part numbers & sp-ecs from Trans/Am Stan. This company protects their ripoff dealers.
WILL NEVER BUY their mdse,
Agree, Ronaz that service people can be mistaken and that some service companies may be gouging.
Certainly I found a popular Dutchess County New York HVAC repair company that responded quickly to service calls but provided me with marginal service at maximal price. Some companies have a business model that establishes a refrigerant-delivery-route business, like the traditional milkman delivery route, but at 100 times the cost of a bottle of milk and without fixing the underlying problem.
In the case you describe, the tech may have just been guessing at the most-likely problem, and the tech does not set prices. But certainly a fundamental first step in checking out an AC that won't start is to confirm that it has power.
If this wiring diagram doesn't match your Rheem Sure Comfort heat pump unit, then see the contact information for Rheem at MANUALS & PARTS GUIDES - HVAC where we also include direct links to wiring diagrams.
Below: a typical Rheem wiring diagram for the AHU. [Click to enlarge any image]
Also see below this very general electrical problem troubleshooting flowchart that works for Rheem as well as other air conditioning & heat pump systems. This chart was found in a "MFA" clickbait page that offered no other diagnostic help.
[Click to enlarge any image]
Question: Mitsubishi split system thermostat display is blank, no error code.
(May 10, 2016) sarfraz said:
I have a one Mitsubishi duct splits
Thermostat automatic going off mode without showing any error code what the resion and how to fix
If the thermostat display is showing blank most-likely it has lost power.
Question: AC was cooling normally for 10-15 minutes then cooling stopped and amps dropped
(May 14, 2016) Anonymous said:
My split AC 1 ton starts normally and the cooling was so good after 10-15 minute the compressor was running but the cooling was stopped and the amp was down to 2 amp what is the problem?
Anon you need an onsite expert to actually say what is the problem, as I can only guess from so little information as a one-line e-text. It's possible that the cooling coil is icing over due to low refrigerant or due to low air flow. Or a TEV can be freezing up.
(May 20, 2016) javed hussain said:
Me interview me jankari Lena chahta ho
Information wants to be in the interview. We agree.
Question: Compressor won't turn on but fan blows, do I need an A/C repairman
(May 27, 2016) Anonymous said:
My heat pump is in a condo, four years old, the compressor wont come on, just the fan is blowing. I have turned the unit off a couple of times, waited a few minutes, than turned back on but no cold air is coming out. Do I need to call a repair man?
If the air handler blower starts when you have set the thermostat to COOL, AND the indoor temperature is above the thermostat cooling-set temperature, AND the outside unit never runs then yes your system needs repair.
Question: Water leaking out the bottom of the air handling unit
(May 29, 2016) Ed said:
Water is leaking out the bottom of the air handling unit in the house
Ed: search InspectApedia.com for AIR CONDITIONER CONDENSATE LEAKS to read diagnostic and repair suggestions. Your system's condensate line may be clogged, or the condensate collection tray may be leaking.
Question: lit match odor when central A/C starts
(July 6, 2016) michelle said:
when our central a/c kicks on there is an odor like a lit match that first comes from the duct. we live in an extremely hot and humid tropical climate in south florida. our home is a mobile home on blocks with the entire unit outdoors. this is a recent development. our temperatures and humidity levels are even higher than 'normal'. any suggestions? thanks!
Question: mix and match condenser and air handler brands?
(July 10, 2016) george said:
can you use a carrier condenser and Panasonic air handlers in a mini ducted system?
Yes in concept, George. But the capacity, refrigerant, and controls must meet one another's specifications.
Question: A/C keeps tripping the circuit breaker
(July 11, 2016) thabo said:
I hv aircon st my office it does not wat to run it keeps dripping circuit breaker
YOu need a service tech on site, sir. The problem could range from a failing control or relay to a seizing compressor motor.
Question: is a rooftop HVAC unit part of the equipment used to heat or ventilate a building?
(July 18, 2016) john simmons said:
is a rooftop hvac unit one of the component parts of the equipment to heat and ventilate a building?
Sure, John. A rooftop HVAC unit may be providing cooling, heating, or both.
Good luck with your test.
Question:proper term for housing for an A/C unit
(July 18, 2016) Anonymous said:
Our ac unit housing needs to be replaced. What is it called?
For a through-wall unit some manufacturers may use the term "through wall sleeve"
2016/07/24 joy said:
Air comes in but not cooling like it usually does. Thermostat set to 75 but saying 82 in house. Changes all filters.
Joy if you search InspectApedia.com for LOST COOLING CAPACITY you'll see a sequence of diagnostic steps that you should take.
Question: specifications for walk-in cooler design, repair, maintenance
2016/07/26 Damon said:
Do you have info on walk in coolers
see WALK IN COOLER REPAIR at inspectapedia.com/aircond/Walk_In_Cooler_Design.php and in the future, please avoid tripling our workload: just ask question on one page, not three. Thanks. - Mod
Question: A/C fan turns off and trips breaker when it's hot outside
2016/07/27 Toni said:
My Bryant air conditioner fan is turning off when the temperature outside is over 105, and it's tripping the breaker. The unit works fine otherwise.
Reply: thermal overload switch?
Toni it sounds as if your system is overhreating and tripping a thermal overload switch; time for a service call.
Is that the exact name of the part? And can someone replace that part themselves? Thank you for all your help.
The thermal overload switch, if present in a motor such as an air conditioner compressor motor, is usually built into the motor, is not a part you'd replace yourself, and is not usually the trouble anyway. The trouble is more likely to be that the motor is overheating because it is overloaded or has low voltage, or is simply failing, e.g. because of a worn bearing.
Some people try testing the compressor/condensor for overheating by wetting and cooling it down with a garden hose when it's hot. (Don't spray directly onto or into electrical components, but wetting the outdoor unit just as if it were raining is OK). If when cooled down the unit runs, that confirms an overheating problem.
Keep in mind that based on a brief e-text I'm only guessing at what's wrong. It would be a mistake to dash out to try to replace any part before we've had an onsite diagnosis of the problem and thus have correctly-identified what repair part(s) is (are) needed.
For photographs of these various air conditioning and heat pump parts, and for an explanation of where these air conditioning components are physically located, see A/C COMPONENTS which discusses and helps you name and recognize various Indoor A/C Components and Outdoor A/C Components
Also see these A/C & Heat Pump Diagnostic FAQs & diagnostic guides
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.
 "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]
 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.
 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.
 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
 Thanks to Joe Panimondo for technical editing, April 2011
 This website discusses these air conditioning and heat pump terms and problems: Air Conditioners: Central Air Conditioning Troubleshooting & Repair Guide: How to Inspect, Diagnose, & Repair Central Air Conditioning: Defects in A/C compressors, air handlers, duct work, and controls. We explain how to inspect & repair central air conditioning systems and for homeowners we also answer basic HVAC questions such as what are the basic air conditioning components? We provide guidance in determining air conditioning cooling capacity & energy efficiency, Troubleshooting air conditioning compressor problems, Diagnosing air conditioning air handler problems, Air conditioning condensate problems, Duct system inspections, defects, repairs, Cleaning air conditioning equipment & A/C refrigerants.
 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.
 HVAC Employment: U.S. Department of Labor website describes HVAC jobs and the employment outlook for HVAC technicians.
[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).
 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. 1701 Pennsylvania Ave NW,
Washington, DC 20006 Tel: (800) 394-5268. Quoting: 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.
 National Center for Construction Education and Research, 3600 NW 43rd Street, Bldg. G, Gainesville, FL 32606, Tel: 888.622.3720, 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.
 The Partnership for Air-Conditioning, Heating, and Refrigeration Accreditation, (PAHRA)
2111 Wilson Blvd., Suite 500
Arlington, VA 22201-3001
(703) 524-8800, 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.
Licensure. Heating, air-conditioning, and refrigeration mechanics and installers are required to be licensed by some States and localities. Requirements for licensure vary greatly, but all States or localities that require a license have a test that must be passed. The contents of these tests vary by State or locality, with some requiring extensive knowledge of electrical codes and others focusing more on HVACR-specific knowledge. Completion of an apprenticeship program or 2 to 5 years of experience are also common requirements.
In addition, all technicians who purchase or work with refrigerants must be certified in their proper handling. To become certified to purchase and handle refrigerants, technicians must pass a written examination specific to the type of work in which they specialize. The three possible areas of certification are: Type I—servicing small appliances; Type II—high-pressure refrigerants; and Type III—low-pressure refrigerants. Exams are administered by organizations approved by the U.S. Environmental Protection Agency, such as trade schools, unions, contractor associations, or building groups.
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
2299 Vauxhall Road
Union, NJ 07083
NOTE: when considering an HVAC training course or school, check the HVAC education accrediting associations listed above.
 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. 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.
 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.
 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
 Air Diffusion Council, 1901 N. Roselle Road, Suite 800, Schaumburg, Illinois 60195, Tel: (847) 706-6750, Fax: (847) 706-6751 - email@example.com - 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.
 Engineering toolbox properties of water - http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html and email: firstname.lastname@example.org web search 09/16/2010
 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™
 "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."
"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]
 FlowKinetics LLC, 528 Helena Street
Bryan, Texas 77801 USA, Tel: (979) 680-0659, Email: email@example.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]
 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)
 Wikipedia 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
 "GE Zoneline® Owners Manual and Installation Instructions, Heat/Cool Model 2900, Heat Pump Model 3900", General Electric Corporation, [copy on file].
 "GE Zoneline® Owners Manual and Installation Instructions, Heat Pump Model 5800", General Electric Corporation, [copy on file].
 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
online ordering: http://www.ntis.gov/ordering.htm
 Yinger R, R Bravo, and D Martinez. 2006 Air Conditioner Stalling Effects Study/Air Conditioner Testing
Procedures. Southern California Edison, Rosemead, California
 Bravo, R, R Yinger, and L Gaillac. 2006. Conditioner Stalling Unit Level Solutions Test Report. Southern
California Edison, Rosemead, California.
 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.
 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]
 Thanks to Alexis Claro firstname.lastname@example.org who maintains a website offering information about HVAC training found at http://hvaced.com/hvac-training.
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]
Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
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