I just replaced the head gasket on my 07 hhr. After reinstalling everything the car runs great, but now my AC only works on max air. When I turn on normal air the compressor will turn off, when I turn it back on to max air the compressor kicks on and blows cold air. I am sure it is a simple thing I missed when I reinstalled everything. Can someone help me figure what that might be?

 

Step one...Go over everything you unhooked under the hood when you pulled the head, it could be a connector that's not fully seated.

Step two...Have the codes pulled, it could be a bad temperature sensor, that will show up as an error.

Also, did you reuse the old thermostat, or did you install a new one? Odd A/C behavior in these critters can usually be traced back to wiring, the temp sensor, or the thermostat.

And check your coolant level, it sounds terribly obvious I know, but low coolant will trigger an "out of range" temperature condition that causes the vehicle to disable compressor engagement.

P.S. to the forum!