I have noticed that my AC compressor cycles on every 15 - 20 seconds when the AC isn't turned on, when nothing environmental is on. It runs for like 4 - 5 seconds and then cuts back off. When I turn the AC on the compressor comes on as it should. I know from experience that a cycling compressor will prematurely eat up the clutch. I have looked at wiring diagrams and can't see why it would turn into a zombie. Any suggestions? Surely this isn't a normal thing. 2000, 1500 Suburban 4x4.

 

This is usually a sign of being low on freon.

 

I agree except that the AC isn't on. When I turn the AC on it functions normally. I'm wondering why it is that the compressor cuts in when it's not turned on, when no environmental controls are on. Cutting on and off slowly is low freon. Cutting on and off rapidly is a superheat condition, usually a weak fan. This is something else, maybe in the switches. Why would a compressor cut on when cooling has not been called?

 

Check to see if there is voltage going to the clutch when it kicks in when it is not supposed to. If not then the clutch is at fault.

 

I'll check that for sure. I expect to find voltage as I can't see any other way that the magnet would engage to pull the clutch in. I have run it through in my mind and all I can come up with is that the computer is sending a call to the compressor for air. Or, there's something in the defrost circuit that's kicking the compressor on. Whatev's.. The worst case scenario is that I have to replace the AC clutch or the whole compressor in the future. That's not a terrible job.

 

auto or manual hvac

 

Is the HVAC set to defrost when the AC compressor turns itself on?

It's my understanding that on most vehicles when the defroster is turned on the AC comes on automatically (unless it is too cold for the AC to operate).

Steve