Help requested. On my 2009 2.4 HHR, AC is not working properly. The compressor clutch is cycling on and off more rapidly than I would think normal and as it cycles, the engine rpms fluctuate quite a bit as if the compressor is lugging the engine. I checked refrigerant and added a little but it is in the normal range.
Vents mostly blowing warm to hot air, but every so often without explanation it will blow cold air. I am suspecting a mixing valve? but not sure. Its weird that sometimes it blows cold air even with the AC controller turned off and just the recirculate mode selected. I have noticed that if I have the temp dial all the way cold and move it anywhere off cold the air will begin to blow warmer to downright hot, but once I do that, the return of dial to cold does nothing, and it will continue to blast hot air.

I know I've come to the right spot for help and ideas. Thanks

 

Recirculation causes the compressor to run, as does either of the 2 defrost positions.

 

I did not know that. I thought compressor only came on if ac selected on the dial and illuminated.

 

It also comes in when defrost is selected. Are there any signs of a leak at any connectors or damage to the condenser? Is the serpentine belt and tensioner in good condition or still OEM?

 

no evident leaks. belt new.
one day I started the car after this was happening and was pleasantly surprised that I had ice cold air. suddenly without touching anything there was a shutter like sound and hot hot hot air was coming out and I could not get it back to cold. Thats why I was wondering about mixer. I don't know where it is, how its controlled, is it fused etc etc

 

Whether the air coming out of the vents is hot or cold, if you have the AC on, the compressor should be running.

You may have a bad HVAC head unit. Or something related to compressor or refrigerant.

 

The temp knob doesn't care if the AC is on or not; turn it toward hot the air will get warmer.
Maybe you should re read the Owner Manual (link in my sig).

 

I’m gonna go out on a limb here and ask , have you changed the thermostat and coolant, then burped the system?

 

Could be a roving air pocket. Have you checked the coolant level, under the pressure cap and the tank?

 

Intermittent symptoms like you mentioned and good pressures high and low side / freon levels indicates to me a restriction that comes and goes.

Running AC on max and recirculate does compressor stay engaged all the time? What does the coolant temp go to before the radiator fan kicks on? Use the DIC to verify with dash gauge.