Procedures for Making Air Conditioning System Temperature Measurements
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This article discusses exactly how and where to measure input and output air temperatures at air conditioning
equipment in order to determine whether or not it is operating properly, as part of checking basic air conditioning system operation
and for detection of air conditioning operating defects. An introduction to air conditioner temperatures and some rules of thumb that are quick and easy to apply in diagnosing air conditioner problems are provided at the preceding article: Air Conditioning System Temperatures.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Procedures for Making Temperature Measurements of Air Conditioning Systems
Air conditioner temperatures that are too high or too low can indicate
specific operating problems on central and portable or window air conditioners. Simple measurements of air temperatures, if
made at the right place, can assist in diagnosing what may be wrong and what repairs may be needed for the air conditioner.
This document is a portion of our website which describes the inspection of residential air conditioning systems (A/C systems) to inform home buyers, owners, and
home inspectors of common cooling system defects.
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 suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
Refrigeration and Air Conditioning Theory: Refrigeration systems rely on two state changes of the refrigerant: gas to liquid, and liquid back to a gas to move sensible heat from the low side of the air conditioning system to the high side. At the evaporator coil heat (BTUs) is absorbed when the refrigerant evaporates (liquid to gas), and at the condenser coil heat is released during condensation (gas to liquid). R12 refrigerant has a boiling point of -21 degF (change of state from liquid to gas vapor) and R22 has a boiling point of -41 degF.
But if you are measuring air temperature close to the evaporator coil or condenser coil you won't record these two temperatures on your thermometer. Rather the temperature that you can record will be significantly affected by ambient conditions. For example, at the evaporator coil the temperature of indoor air entering the coil, the distance between the coil surface and the thermometer, the air velocity, and other factors will produce a temperature reading that is different from and certainly higher than the boiling point of the refrigerant entering the coil.
While we may form an opinion about just how cool the air should be right at an evaporator coil, or inside of an air handler supply plenum, most diagnostics look for temperature differences between air entering the air handler and air leaving the air handler to evaluate what's going on in the system.
NOTE: an air conditioning technician has more precise tools to evaluate the condition of a system such as gauges to measure the pressures on the high side and low side of the system and an ammeter to measure current draw of the compressor.
How to Examine Air Conditioner Temperatures
Temperature Measurements & Observations at the Room Thermostat
Air conditioner thermostat settings: observe the settings on the wall-mounted room thermostat (assuming you've already
established that the switches and controls have turned the system on and that it is in cooling mode and has
been operating for half an hour or longer.
Note the set-temperature (the cooling target set on the thermostat) and note the ambient
temperature (the actual air temperature close to the thermostat). Most thermostats will tell you both the set temperature and the actual room temperature. These
should be within 2-3 degrees F. of one another if the system has been in operation for several hours and if
the air conditioning system is working properly and has adequate capacity and of course if you're using it normally
with the building windows and doors closed, supply and return registers open, filters not clogged, etc.
Temperature Measurements at the Evaporator Coil in the Air Handler
How to Measure Air Conditioning Register outlet temperatures using a dial thermometer probe:
we simply wedge the probe of our dial thermometer between the
vanes of a ceiling supply register, or drop it probe-first through the slots of a cool-air supply floor register
where we leave it for at least five minutes. Sketch courtesy of Carson Dunlop Associates.
We select a supply air register closest to the air conditioning equipment if
at all possible, and if there is access we confirm visually that the duct is not crimped, blocked, and by simple
feel, we confirm that air is flowing out of it.
We use tissue or toilet paper to confirm for skeptical owners that
the direction of air flow is "in" at a return register and "out" at a supply register since sometimes this
can be confusing to a novice.
Measuring Air Conditioning Duct temperatures using a dial thermometer probe: if there is not an existing
duct opening such as a foil-covered hole or a removable plug, we drill a 1/4" diameter hole in the sheet metal
of the duct. BE CAREFUL not to drill where you can damage a refrigerant line, coil, wire, etc. After inserting
the probe into the hole for measurement, waiting, taking our measurement, we close the hole using a square of
adhesive foil tape, duct tape, or snap-in plugs sold for that purpose.
Temperature Measurements at the Condensing Coil & Fan/Compressor Unit
Measuring temperatures at an Air Conditioning Compressor: By holding the thermometer's probe in any
air path (and patience) it is trivial to measure ambient air temperature, air temperature flowing into the
condenser unit at the condensing coils, and temperature flowing out of the condenser at its fan output (keep
the probe out of the blades!)
Measuring Air Conditioning Temperatures Using an Infrared Thermometer: permits measurement of
surface temperatures such as the surface of a metal duct (is it insulated?), surfaces of
refrigerant suction and high pressure lines (do we know target temperatures?), or surfaces inside
a building.
We use infrared temperature scanning of building surfaces to scan for currently wet conditions
(this won't tell you if there was previously a leak that has since dried, leaving behind a mold problem),
and to scan a building for air infiltration or ex filtration losses, and to scan for the presence or absence
of insulation (there must be a good difference, perhaps 20 degrees F, between indoor and outdoor temperatures
to make this check accurately) but we do not use infrared scanning on air conditioning equipment except to
look at the surface temperature of a heretically sealed compressor or to check for hot electrical connections
in the panel or switch box.
Remember that when using an infra-red sensor you may not be reading actual
surface temperature unless you're measuring a black surface. Some scanners are provided with a black
crayon or marker to make a spot to be used for temperature sensing. These devices are excellent, however,
for comparing the temperatures of different surfaces.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
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Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.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:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
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 Home Reference Book, a reference & inspection report product for building owners & inspectors.
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.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- 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.
- 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.
- 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
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.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 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.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- 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
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.
- 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
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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