When I turn on the AC in my Sierra, the compressor goes on for just a short time then turns off again, then goes on then off, on and off. Under the dash, there is also a clicking which I presume is the thermostat. I'm guessing that the thermostat here is the problem but thought I'd ask for opinions.

Something that might be related is the fact that a few electrical bits are not working either. I just noticed this after a friend had borrowed the vehicle for 2 weeks, so I don't know if it all happened at once. Anyway, the radio is completely off (no power), the dome light and reading lights are powerless, as well as the cargo light.

I'm wondering, then, if perhaps these all run from the same battery cable that has finally worn out? Any thoughts are appreciated.

 

Need pressure readings of AC system. It could just be the relay for the a/c system clutch

 

check all the fuses you probably have a blown fuse causing the dome and cargo lights not working possible the radio also, suspect the a/c is low on freon if its cycling on and off alot probably have a leak somewhere in the system.

 

If you've lost just enough refrigerant to be right at the trip point for the low pressure switch, the AC will cycle on and off like that. Put a manifold gauge set on there and see if you're low on refrigerant.