Myth or Fact


Old 01-03-10, 07:57 PM
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Myth or Fact

The myth is that car Air Conditioning systems wont function when the outside temperature goes below 60 degrees.

Is there or isnt there a temperature sensor that prevents the a/c clutch from energizing if it's too cold outside?

My a/c clutch energizes when the defrost is selected but not when the a/c is's 25 degrees here.

I'm asking this because I just bought an '06 Pontiac with this condition and wondering if the system needs to be serviced or is normal.
PS. it came from Florida and has 30k miles.
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Old 01-04-10, 04:06 AM
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Your A/C clutch will energize when on defrost because conditioned air is dryer than heated air and will "dry" the windshield better during humid times. It will disengage as you move the heat further to the hot side. I know of no "sensor" that prevents the compressor clutch from being energized purely for temperature reasons, except that if it has an automatic temperature setting it won't energize, since the temperature has been attained at 25 degrees.
Old 01-04-10, 10:09 AM
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I believe that the owner's manual for my 2005 Mazda states that the AC operates automatically on the defrost setting but will not come on below 20 degrees F. Might be something I read on a Mazda forum though. I'm sure it's different for different cars.
Old 01-04-10, 11:03 AM
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On my car and truck, there are no sensors to prevent the A/C from working when it is cold.

As a matter of fact, I turn on the A/C when it is cold outside and the windows start to fog up on the inside. This clears them right up!

And it is a good idea to run the A/C every now and then in the winter to circulate the oil.

BUT there are new automatically controlled A/C systems which have temperature sensors all over the place including outside. I would imagine that these would not turn on the A/C unless it was needed. And they may or may not turn on the A/C for defrost?

Basically they design vehicles every different way you can imagine. Everything constantly changes. Who knows what all is out there?

These days everything is electronic. And they adjust the engine speed based on what accessories are turned on. So they will tie things like A/C in to the engine computer.

On my car for example, the switch to turn on the A/C actually goes to the engine computer. Then the engine computer is what activates the compressor relay and in turn the compressor for the A/C under the hood.

By doing this, then engine computer "knows" the A/C is on and can adjust the idle. Also under certain circumstances the engine computer will turn off the A/C compressor to give the engine more power. (Like with wide open throttle say when passing a car.)

With that said, A/C systems can be complex. I would not attempt to work on one without the factory service manual and electrical diagrams manual (order from dealer). This will give a complete description of operation. Show all the electrical components, wiring, etc.

Then working on A/C (charging the system) when it is cool outside is a challenge! The system needs to be hot to keep the compressor going so you can charge the system. I have done this by turning on the inside air to high fan and heating on full blast, recirculate, and A/C on. (This keeps hot air going into the evaporator inside the car.)

Then placing a piece of cardboard over the condenser coils in front of the radiator. This keeps the refrigerant from cooling down too much, so the compressor keeps running.
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