A/C Compressor Not Running
 

My daughter informed me last night that the A/C hasn't been working on her HHR. It apparently was good and cold on Wednesday and not functioning at all when she started it on Thursday. I was able to check the following before she took the car back to school.

- A/C light comes on when button is pressed
- Compressor is not running at all
- Engine does seem to change tone a little when A/C button is pressed
- A/C fuse is good
- A/C relay is good (swapped with another)
- A/C charge is 70 on low side and 100 on high (without compressor running, obviously)

I'm thinking this looks like a compressor issue, or at least the clutch. Am I on the right track, or should I invest in professional diagnosis before ordering a compressor? Thanks!

Any CEL codes, a check engine light code such as P0128, will disable the A/C.
Also a toasted blend door actuator can cause similar problems.
I’d also check the cabin air filter, a good idea to change that anyway.

95% of the time it is because the t-stat is not warming the engine up enough. Coolant temp should get up to 180F in less than 5 minutes (the computer has a time limit) and should stay ABOVE 180F.

We'll have to check that. No issues with any codes that I know of, but didn't really pay attention to how fast it got to operating temp. I didn't know that would affect the a/c.

Underhood fuse block:
#9 Diode
#22 Fuse
#15 Relay

BCM:
#10 Fuse
#16 Fuse
#30 Relay

These are all associated with the HVAC. Try swapping with known good fuses/relays(from working systems). Not sure how to test the diode.

Don't forget the pressure switch.

Yep. How do you test a pressure switch?

short across the connectors.

Everything seems to test good so far. One thing I did find is that there appears to be power to the compressor connection when the AC is turned on. So if there is power there, is it safe to assume that the compressor clutch is probably bad?

If the clutch is getting 12V it should be turning. You should check the diode first though, it is in the under hood fuse box.

It should allow current in only 1 direction; so check for continuity in both directions with an ohm meter.