AC Mystery

[jsnevets]

This morning I got in my car to go to the store. The AC was on but all I got was warm vent air. I pressed the button to turn AC on and off several times. The light would change but I didn't notice any change to the load on the engine. After I left the store and got in my car, the AC was then working fine again. Is this some electrical gremlin or an omen of something worse?

[BNaylor]

Unless the issue reoccurs I wouldn't worry about it. Since you felt no load obviously the A/C compressor clutch wasn't engaging. It could be caused by a low refrigerant charge or electrical issue such as the climate control head unit, A/C clutch relay or the A/C clutch coil just to give you an idea.

[doctorhrdware]

I have a thought, is it possible that the freon it just a touch low. So when the car warms up, which causes the freon to expand, and it allows the pressure sensor to activate which causes the ac to work.

[BNaylor]

Originally Posted by doctorhrdware

I have a thought, is it possible that the freon it just a touch low.

The lo/hi pressure switch will activate with under 1 lb of R134a refrigerant so it would have to be more than a touch low you think?

[thisnametooktolong]

It could be just a little low on refrigerant OR
I have seen it a million times that the clutch on the compressor is worn and will not engage. It starts out intermittent and then goes Full time. Turn on the AC check the compressor to make sure that it is not spinning, then carefully take a stick and push the clutch in. If it grabs and works that is a clutch problem. If that does not work, jack in a noid light and see if it gets power. There are a number of pressure relays that need to be closed for the pump to run. If you noticed that some times the darn thing would freeze you out and others it did not work well a clutch may be your problem

They are

Power steering high-pressure switch (they do that to save the belts)
Then there are 2 or three switches on the A/C. a high-pressure cutout and a low-pressure cutout, on the high side. There is also a low-pressure cutout on the low side. They are meant to protect the pump if the expansion valve gets plugged or there is not enough refrigerant to move the oil around.

Usually if it is low on refrigerant the pump will short cycle. That means that it will pump until the pressure drops and opens one of the switches.

[BNaylor]

Originally Posted by thisnametooktolong

Then there are 2 or three switches on the A/C. a high-pressure cutout and a low-pressure cutout, on the high side. There is also a low-pressure cutout on the low side.

Incorrect. There is only one switch assembly located by the accumulator on the drivers side which is a combination lo and hi refrigerant pressure switch controlled by the PCM (powertrain control) module. Also, the 5 volt reference voltage to the switch is provided by the PCM module.

Originally Posted by thisnametooktolong

Usually if it is low on refrigerant the pump will short cycle. That means that it will pump until the pressure drops and opens one of the switches.

On a GM/Harrison V5 variable displacement compressor? I don't think so.

[jsnevets]

Thanks for all the replies. So far the problem has not happened again. The AC cools pretty well so I don't suspect it is very low on freon. I'll post again if the problem comes back.