Air conditioning only works when the car is hot

I live up here in the great state of Montana and for two years now have been battling a problem that nobody seems to have heard of with my cars air conditioning (2006 Ford mustang v6 auto). During the summer’s here it never gets sweltering hot…just hot…but still hot enough to need A/C. The problem is, when I am doing in town driving, I never can get the car hot enough to turn on the A/C. How do I know its heat related? If I drive on the freeway for an hour, the A/C starts working…or in the winter, after an hour the compressor kicks in for the defroster…also, when I had the car in Vegas at 105 degrees…the ac turned on after 10 minutes…also, recently the stang’s thermostat stuck mostly shut and caused the car to run really hot…A/C worked fine when the car was overheating, but obviously I turned it off. :slight_smile: jumped low pressure and high pressure cutoff switches to rule them out, recharged the coolant, checked diodes, relays, etc… all work fine after one hour…or when hot…otherwise I get no power to anything. why in the world is my car doing this and how do I fix it? Nobody in town or on the internet seems to have a good answer! Thanks for your help. :slight_smile:

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Seek advice from a a/c specialist…I am sure he will find the problem in no time.

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I assume you mean no power tothe compressor clutch. Is this clutch controlled by a module?..thePCM? If so, that module might be faulty.

The problem might be caused by a faulty AC clutch cycling switch.

As stated in the article, this switch can be effected by temperature.


I have a low pressure side sensor…what I read to do with that is take the plug off of it and jumper the wire with a paperclip. It connects the circuit and acts as an override to turn on the clutch. If I jump the plug like that, nothing happens. If I repeat the same test once i know the ac is working, it functions normally.

That is correct. I’ve put a voltmeter to the compressor clutch, and the relay circuit for the compressor clutch in the fuse box. Neither recieve power at all until the ac is functioning normally after an hour…what is the pcmr and where do I find it and test it?

Do you mean neither the signal to the relay nor the AC clutch power wire to the relay has power? You need to back-track from the AC clutch relay to find the failure. The PCM (powertrain control module) is a computer in a box. I don’t know where it is in your car. You need to get a wiring diagram for your car’s AC system.

Maybe it is the AC thermostat function that’s failing. The AC turns on and off depending on the temperature inside the car. Maybe it thinks the temperature inside the car is already cold enough, so it won’t turn on. Maybe monkey around with the AC temperature control knob or lever, see If you can get it to kick on that way. If so, you’ve narrowed down the problem at least. If you can find where the temp sensor is located for the AC thermostat, try heating it up with a hair dryer, see if that causes the compressor to kick on, another idea.