Wifes07LT

It seems like more and more often, I get the phone call from my wife while she is driving somewhere in the HHR, during which she informs me it is happening again..... What is happening? Simultaneously, the temperature gauge "flatlines," going to the lowest temp position, and the air conditioning stops blowing cold air. After talking to her and experiencing it myself a few times, I have determined there is no pattern to this, it is truly randomly intermittent. It will happen, then the problem will go away sometimes on its own, and sometimes after turning the car off then back on, but sometimes that won't even help. It has been a long time since I worked as a mechanic, but this seems like a weird problem, it seems to me the two shouldn't correlate. Anybody have this problem before?

whopper

Believe it or not, it's the thermostat that has jammed open. When it jams open, most likely due to a deteriorated rubber gasket on the movable valve, the engine is then slow to warm up.

The computer monitors the temp as it warms up, and if it does not warm up fast enough, it blanks out the digital temp with "----", and the analogue gauge drops to the bottom, and to top it off the A/C is disabled.

Depending on the severity of the problem, the computer MAY light up the Check Engine Light - but not always. If the CEL lights up, download the diagnostic code - code P0128 indicates "P0128 Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature".

Several of us have had the thermostat jam open like this - Here is a link to a how-to-on replacing the thermostat:

https://www.chevyhhr.net/forums/how-tutorial-library-21/how-save-%24350-00-thermostat-replacement-2-4l-p0128-24493/

An article about the symptoms you have been encountering:
https://www.chevyhhr.net/forums/problems-service-repairs-42/temp-gauge-c-stoped-working-37675/

The cooler the weather, the more frequently it will occur as it will take the engine even longer to warm up.


Hope this helps.

whopper

Oh, and being a new member (Welcome) - you might find this link of common topics/problems/fixes handy: https://www.chevyhhr.net/forums/problems-service-repairs-42/list-common-problems-questions-related-links-38985/

Wifes07LT

I forgot to mention I've gotten that code a few times, but before this issue started happening. But this will just randomly happen after the car is warmed up, like she will be driving for 30 minutes on the expressway and suddenly the gauge stops and the A/C starts blowing hot.

Thank you for your help, I will replace the thermostat this weekend. It's a very weird diagnosis for a very weird set of symptoms!

donbrew

Overheating could also be a cause. You need to know the coolant temp. look at the analog gauge, and be sure that there is coolant, when it is cold open the pressure cap the coolant should fill the hose, as well as having coolant visible in the overflow tank. You could be having a bad head gasket, but that is another set of everything.

Not weird, when the computer senses a coolant problem it starts shutting things down in an attempt to live and to alert the driver.

mojobubba

Mine does the same thing but also blows the a/c clutch fuse. No noise or smoke from the belts.

donbrew

Has anybody thought of checking the clutch circuit? Sounds kind of like the A/C clutch has shorted out.

mojobubba

UPDATE... No noise or smoke from the belts as if the A/C clutch is locked up. I have interchanged the A/C clutch relay (#15) with the rear gate release relay (#18) and still no cold air. The rear gate release will work with either #15 or #18 relays.

Checking out the A/C clutch circuit now...I'll be back! I think you may be right.

donbrew

If it ain't locked up then it's free wheeling. duh.

The clutch is "normally" disengaged, so if it's broke it won't engage. Worn out, foreign object, fried coils etc.

db/sb

Ease up. If you had corrected your statement in post #8, post #9 wouldn't even exist.