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AC stops blowing cold after reaching 60mph

Posted: Tue Oct 22, 2019 9:42 pm
by tireseus
2011 sport SLS bought new. Has 93k miles on it and for the last 6 months, when I reach over 50-70 mph the ac will stop blowing cold and actually blow hot. I am in Houston, so you can imagine how terrible that would be in the summer.

The mechanic has replaced compressor, the ambient air temp sensor, the dash console and pretty m uch everything else. He tells me there is a sensor that switches the fans on and off, but says hes replaced it all. Is this a problem with the main computer?

AC works great otherwise, driving around town and such.

Re: AC stops blowing cold after reaching 60mph

Posted: Tue Oct 22, 2019 10:13 pm
by G13b
Maybe its low on refrigerant, putting a new compressor also means needs to charge a refrigerant.

Re: AC stops blowing cold after reaching 60mph

Posted: Wed Oct 23, 2019 12:27 pm
by Ronzuki
Typical mechanics are not A/C technicians. I've already been in garages w/ the 'juice-it-up' Freon/oil cans sitting around. We can perform that temporary improper fix ourselves, and I have. I certainly wouldn't have an auto mechanic taking a look at my home's heat pump systems. The mere fact he's replaced everything w/o success is indicative of this fact. There are specialized automotive A/C shops around...you just have to find one near you. Anytime you crack open a refrigerant line, the correct (and only) way to recharge the system is by pulling a vacuum and recharging utilizing the proper equipment that 90+% of Joe-Blow mechanics don't have, never use, likely never seen, and therefore were never trained properly in how to handle A/C. Just visit an HVAC forum and have a look at the posts. You will quickly realize that HVAC (doesn't matter...car, house, appliance) is an entirely fickle specialization all its own. Just like all this nifty whiz-bang automotive automation. The sooner the auto industry recognizes these facts (likely never), the better off we consumers will be.

Re: AC stops blowing cold after reaching 60mph

Posted: Fri Oct 25, 2019 1:37 pm
by bdleonard
tireseus wrote:2011 sport SLS bought new. Has 93k miles on it and for the last 6 months, when I reach over 50-70 mph the ac will stop blowing cold and actually blow hot.
When you say "blow hot", do you mean warm outside air or do you mean hot air as if you had turned on the heat in the car?