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Following the guidance from this Q&A, I measured the output temperature of my 2012 Town and Country A/C. Under the test conditions proscribed, with outside temperature of 87°F and 55% relative humidity, the following observations were made:

  • When temperature set to maximum cold ("LO") and blower set to minimum speed ("1" bar), the output air flow is 42°F.
  • When temperature set to maximum cold ("LO") and blower set to maximum speed ("6" bars), the output air flow is 60°F.

I am not expecting a nearly 20°F rise in temperature with the blower going. This explains why the A/C feels "cool" to me under normal operating conditions (which is some where in the middle of my experimental range).

What's going on here?

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1 Answers1

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Welcome to the wonderful and wacky world of thermodynamics.

A volume of air has heat. For example a gallon of air needs a certain amount of cooling to drop from 87 degrees to 42 degrees.

An AC evaporator can absorb heat at a constant maximum rate. When the blower is on low and lets say flowing one gallon of air a second, the evaporator is able to drop its temperature from 87 to 42 degrees. Now you turn the blower to high and the flow rate goes up to six gallons a second. The cooling rate of the evaporator has not changed, it is still pulling in a fixed amount of heat. So when the evaporator could cool one gallon to 42 degrees, it now cools six gallons to 60 degrees in the same amount of time.

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