Photograph of a dial thermometer reading a high output temperature at an air conditioning compressor HVAC Air Temperature Measurement
What Instruments Are Used to measure Air Conditioner or Warm Air Furnace Operating Temperatures?

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How to measure A/C temperatures: this article describes how 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.

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.

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List of Types of Instruments Used to Measure Air Conditioning Temperatures

If your air conditioning or heat pump system has lost its cooling capacity or wont' start see LOST COOLING CAPACITY and also REPAIR GUIDE for AIR CONDITIONERS and see How to determine the cooling capacity and 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.

If you need to know the normal operating temperatures of air conditioners & heat pumps and where those temperatures are measured, see OPERATING TEMPERATURES HVAC.

Dial thermometers such as the dial face shown in the photograph at the top of this page are inexpensive (typically less than $10.00) and very simple instruments which combine a bimetallic spring, a dial face, and a stainless steel probe which can be inserted into A/C systems at key points (below) or in some cases simply held in an air stream. The thermometer can take a couple of minutes to stabilize, so you should keep it in position until the dial indicator stops changing. Dial thermometers vary in accuracy but can easily be calibrated (using boiling water).

Don't choose a dial thermometer whose temperature range is much greater (say 0 degF. to 212 degF.) than the range that you need (say 30 degF. to 100 degF.) since the smaller range thermometer will be more accurate in determining the temperature.

Digital thermometers work much like a dial thermometer but include a digital display of temperature (and require a battery). Digital thermometers cost a bit more, typically around $25. to $130.

Air flow thermometers are electronic devices similar to a the temperature probes above, but their probe ends in a loop through which air passes to provide a more rapid readout of air temperature. However these devices are not easily inserted into duct work as a larger probe opening will be required.

Infrared temperature measurement devices have the feature of being able to measure surface temperatures from a distance but are not used to make direct measurements of air temperatures

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