VetteVinnie

**FINAL SOLUTION: Final diagnosis and corrective action was to replace the expansion valve in the A/C system. It was not properly regulating the pressure.

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**UPDATE** - I picked up the car around noon, and the problem was still there, so although the alternator may have been having a problem of which I was unaware, it was NOT the cause of this issue. Disregard this information. The car is back at the dealer for additional debug.

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I had a thread awhile back talking about the A/C cutting out at idle when the temps and humidity got really high. Car wasn't setting any codes. It would just all of a sudden blow hot air, usually at a traffic light or just waiting on the wife while she shopped. As long as the car was moving, everything was fine. It had the GM techs really baffled. Took three trips to finally demonstrate what was happening. All of the pressures in the system were fine.

Well, thankfully one of the service managers happened to be standing behind the car at some point during the failure and noticed that the tail lights started to flicker right before the compressor kicked off. Replaced the alternator, and all is well. Wasn't an A/C problem at all. Didn't set a code because the voltage didn't drop below the threshold, just low enough to kick off the A/C.

So keep this in mind if you ever start having problems with the A/C suddenly blowing hot air in high ambient temperatures and humidity while the car is idling.

songman3

Thanks for posting that - very interesting!

BlaznZ06

EViLalternator

Coldmale

I have exactly the same problem. Must check the tail lights. Mind you, we did reduce the A/C pressure from 380psi to 250. That seems to have helped. Needed 8g less gas

VetteVinnie

You could also watch the alternator voltage. It was occurring when it dropped to between 9 and 10V.

It all makes sense, really. Heat creates resistance, so extreme ambient temperatures would expose any weakness.

Coldmale

My charging is fine - 13.8 - 14 always

I do live in Bahrin, todays ambient temp 41deg Centigrade

That is a starin on all the engine not just the A/C

John

VetteVinnie

I updated the original post. The alternator apparently was another unrelated problem. Car was still acting up after I picked it up from them. It's back in their hands now.

So, alternator was not affecting A/C operation at all. Dealer misdiagnosis.

Coldmale

OK. Maybe the same as mine, so do the following:-
1. Put on a pressure guage and check the low and high pressure, should be between 30 and say 250. Mine was 380psi.

He released the gas, cleaned out the compressor and refilled with the specified weight of gas. 0.050kg I think

He took pressure again and it was 300psi, so he let 0.008KG out and the pressure dropped to 249

Thats where it is today and it works

What has also happened is that now the cooling fan does not come on at low temp, as it was being primed by the A/C pressure

Wonderful contraptions these cars

John

GOLD72

Friday morning, I went to the office parking garage to go home for the weekend. Immediately upon starting the car (in the shade due to being inside an open parking garage), the HVAC blew hot moist air. That seemed strange to me at that moment but I thought within a few seconds, the AC would be enabled and starting cooling the car. Wrong. Drove several minutes with nothing but hot moist air blowing furiously out of the vents. I tried putting the controls on AUTO rather than manual with no good effect. Then I punched the AC Cancel button and got the AC Cancel Icon. Then I hit the AC Cancel button again to reenable the AC. Success!!! I guess one of two things happened. Either the BCM was confused and needed me to cycle thru the controls to clear the problem or the AC compressor clutch failed to engage the compressor and cycling the controls de-engergized and then re-energized the clutch and allowed it to engage finally to run the compressor. No more problem since last Friday. I have never seen this happened before on a modern corvette.

VetteVinnie

Final diagnosis and corrective action was to replace the expansion valve in the A/C system. It was not properly regulating the pressure.