Probably the temp sensor. The first code does not always trigger a CEL. Check for codes anyway, when the reading is --- and AC won't work. Same code for temp sensor and t-stat. "normal" operating temp is 180F - 195F, you may have other problems. Have you checked the coolant level under the pressure cap? Is the t-stat a ACDelco 131-158?

 

When I was guessing the temp, I was guessing. Maybe it was 189 and it seems to open at 200.

I believe I replaced the temp sensor at the same time (did timing chains and water pump at that time around Christmas 2016), but I am not certain. IIRC, the hardest part about that is just reaching it. Seems like a reasonable thing to do. Will check the fluids.

Coolant level under the cap looks good. Overflow container looks low. Will add some. Squeezing the hoses does not affect the levels (rises when I squeeze and goes down when I let go).

My OBD2 reader does not work on this car for some reason. I have been relying on lights and I have zero indicators. So, if I am hearing you right, you believe the HHR will disable the A/C when it believes the cooling system is not working right.Is that true.

Thanks for the ideas. I will start with the basics of the cooling system and go grab a sensor this evening.

 

Thinking you are right. The portion of the sensor where the electrical connector attached seems to rotate as I pull the connector off. That doesn't feel right.

 

If the coolant does not warm up fast enough or is too low the AC will not function and the reading will be ---. Usually there will be a P0128 code either current or pending. If the sensor is broken the computer thinks the temp is ---.

The t-stat is supposed to open when the temp rises to 180F and closes when the temp reaches 180F. It's job is to keep the temp above 180F. It is the fans job to cool it, it turns on at 219F and off at 180F.