I got myself a brand-spankin new analog thermometer to benchmark my A/C now that we’re getting back in to our warm season (in KY, anyway).

Do I need to calibrate this thing with ice water? Directions on the packaging didn’t mention it. I didn’t want to assume it was good to go.


No. it’s just a room thermometer. check it with any other thermometers and you will see that none will be exactly the same.


What am I missing? Why do you need a thermometer? Isn’t the right setting the point where you feel comfortable, rather than saying “it needs to be ‘x’ degrees”?


Lots of people put thermometers in one of the outlet ducts of the vent system to monitor the AC performance. Myself included.



You could put it i an ice bath to check it. Is it an alcohol or mercury thermometer? If so, calibration isn’t needed.


An A/C system that is cooling to only say, 45 degrees instead of 40 degrees may indicate an undercharged system, which could eventually damage the compressor.

So the point is to make sure that the a/c system is performing correctly, not to determine what setting is “comfortable.”


Two things. First, checking that the thermometer is accurate is never a bad thing. The second is that nobody can tell you the proper output duct temperaturefor any A/C system. That depends on the type of compressor, refrigerant, outside temp, inside temp, relative humidity, fan speed, distance from the evaporator, and condition of the vehicle’s cooling system. Most systems will only cool 30 Deg from outside temp.


Calibrating with ice water is an excellent idea. It is unnecessary, since your purpose does not require any great accuracy, bit you have reassurance your instrument is working correctly.

Your factory service manual will give you the correct testing procedures, which differ for various models. If you don’t have the manual, contact the regional office, customer service department, technical division.