A/C compressor - Always on

[barryware]

Hi.. I searched the forums and found that there is a switch on the back of the air selector dial.. Floor , floor defrost, full defrost, etc... that allows the compressor to run when in defrost mode even though the AC button is not pressed or illuminated

My AC compressor seems to be running even though the AC switch is not on. I had a similar problem when my water pump was failing.. When I went to change the pump, I found some pink crusty stuff had fallen into the compressor clutch and kept it engaged even though electrically, it was not supposed to be. A squirt with the garden hose cleared out the crud and at the time, the compressor & clutch worked as expected.

Does the compressor run when in floor / defrost mode or just full defrost?

I typically keep my selector in floor / defrost mode. I know the compressor is cycling cuz when I checked this, the pipes change temperature and I can see a few bubbles in the sight glass as the compressor turns off. My compressor must be a real quiet one because I can not hear it clicking on and off.

If the compressor is allowed to run when in floor / defrost mode, I don't have anything to worry about. If it is only supposed to run when in full defrost, I have a problem. As I am sure most know, there is no relay for the compressor.. Everything goes through the AC amplifier.

EDIT: 2007 US hatchback

[WeeYari]

Compressor runs in both defrost modes.

[barryware]

Compressor runs in both defrost modes.

Good to hear.. Also I now know where my gas milage went. I thought is was due to the cold weather..

[WeeYari]

...in a way, it is...

[barryware]

I played with it on the way home from work.. Indeed... Floor & defrost or full defrost, the compressor runs. The bullet between floor only & floor/defrost, it does not.

I have no idea why I didn't notice this before. What made me look, was the radiator fan was running when I would not expect it to. I heard it when pulling into the garage a few days ago.

I don't remember any of my other cars, whether US or import, the compressor would / could run if the enable switch was not on.

Anyway... Saves me a trip to the dealer for service thinking there was something wrong.

[severous01]

defrost requires the ac compressor because the condensor cools and humidity is applied to the fins and sticks....draining all the water out of the air...making the air dry. so....defrosting the windshield with wet air wont work, so you need the ac on to cool the condensor and wick the moisture out of the air.

otherwise, you're just moving wet air onto the windshield....making it more frosty.

if you have it on MAX AC, or any defrost mode, the AC comes on automatically even if the ac button is off.

[auxmike]

I hate this feature. Never had a car with this before, never missed it!
I don't like being "forced" to turn on the A/C when it's 20F outside!

[Tom48]

A/C compressors use to go out pretty regularly every spring. A result of not being used for 2 to 4 months, depending were you lived. The compressors were huge compared to the ones we have now. These smaller ones don't have that much pull down on our engines and have little effect on our MPG. By having them run with the defrost in the winter we have fewer failures in the spring. I have checked the MPG with the A/C runing and with it running and I get the same 35MPG either way..