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2010 GMC Sierra A/C blows hot air on acceleration

philmitchell

By philmitchell
in Ask A GM Technician

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philmitchell New Member

philmitchell

Posted
Posted

2010 GMC Sierra 5.3L V8 FFV 6-speed Automatic 6.6 ft. Bed - 17k miles

 

My truck above - when I accelerate, many times the a/c goes to blowing hot air. If I am cruising say at 65-70 and speed up any at all the a/c immeadiately begins to get warmer. One dealer I called told me that this is a built-in "feature" to give you more HP on acceleration - I doubt this as the compressor doesn't pull that much.

 

In the "olden days" this was caused by a defective a/c module in the dash, which caused a sort of vacumn leak closing of the intake vents.

 

What would cause it on this truck and how do I fix it? If it is some kind of design feature, how do I override it?

 

Thanks,

Phil

thearborbarber Enthusiast

thearborbarber

Posted
Posted

There is programing in the pcm to temporarily shutoff the a/c. It's to keep it from overspeeding the a/c compressor. When I tuned my camaro it was based in throttle position and on the corvette it was based on rpm.

Jsdirt Senior Enthusiast

Jsdirt

Posted
Posted

I thought it was only supposed to cut the compressor when the pedal was mashed to the floor .... 100% throttle in other words. I haven't an answer for that one.

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

Easiest way to verify that it is the compressor being turned off is to simply turn the a/c off yourself while cruising on the highway and see if the air temp changes the same amount as when you floor it. Just press the fan speed button to turn compressor off.

SouthCo Senior Enthusiast

SouthCo

Posted
Posted

Has it always done this? If still under warranty take it in. I don't notice mine getting hot when accelerating. I have the same truck with 20k miles. Now if your talking about when holding the pedal to the floor, I can't say. I don't really drive like that.

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

for some reason i cant copy and paste the description and operation of the air delivery system ,it in it says that the PCM disables the a/c for a number of reasons,one of which is 100% throttle ....

Mikeb52r Enthusiast

Mikeb52r

Posted
Posted

Take it in for warrenty. You don't stay in the throttle long enough for it to blow hot air. There is a problem with the programming or a bad actuator. I had my actuator replaced within 10k miles and they had to reprogram.

  • 3 weeks later...
philmitchell New Member

philmitchell

Posted
  • Author
Posted

Well I took this truck into the dealer since it is still in warranty, and they said there is absolutely nothing wrong with the A/C. The tech helpfully said that I should expect the a/c air to become slightly warmer when it accelerates. There was another guy there who has a truck like mine and he says his behaves like this also, however he conveniently works for the dealership. I pointed out that I can decelerate for 20 seconds and it is blowing warm air the whole time - apparently this is by design.

 

I am totally dumfounded - leave it to GM to take a concept that has worked for years and find a way to screw it up. Perhaps I drive the truck too hard - with the 6 speed tranny it seems always to be in too high a gear, so I do accelerate aggressively. The truck manual actually says to floor it if you need to downshift and speed up quickly, but I never accelerate to the point of flooring it.

 

Now I need to find a way to bypass the connection between acceleration and A/C compressor.

gmtech4 Senior Enthusiast

gmtech4

Posted
Posted

Well I took this truck into the dealer since it is still in warranty, and they said there is absolutely nothing wrong with the A/C. The tech helpfully said that I should expect the a/c air to become slightly warmer when it accelerates. There was another guy there who has a truck like mine and he says his behaves like this also, however he conveniently works for the dealership. I pointed out that I can decelerate for 20 seconds and it is blowing warm air the whole time - apparently this is by design.

 

I am totally dumfounded - leave it to GM to take a concept that has worked for years and find a way to screw it up. Perhaps I drive the truck too hard - with the 6 speed tranny it seems always to be in too high a gear, so I do accelerate aggressively. The truck manual actually says to floor it if you need to downshift and speed up quickly, but I never accelerate to the point of flooring it.

 

Now I need to find a way to bypass the connection between acceleration and A/C compressor.

last part.....not happeneing ,,,,computor(s) is in the way

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

Well I took this truck into the dealer since it is still in warranty, and they said there is absolutely nothing wrong with the A/C. The tech helpfully said that I should expect the a/c air to become slightly warmer when it accelerates. There was another guy there who has a truck like mine and he says his behaves like this also, however he conveniently works for the dealership. I pointed out that I can decelerate for 20 seconds and it is blowing warm air the whole time - apparently this is by design.

 

I am totally dumfounded - leave it to GM to take a concept that has worked for years and find a way to screw it up. Perhaps I drive the truck too hard - with the 6 speed tranny it seems always to be in too high a gear, so I do accelerate aggressively. The truck manual actually says to floor it if you need to downshift and speed up quickly, but I never accelerate to the point of flooring it.

 

Now I need to find a way to bypass the connection between acceleration and A/C compressor.

 

Go back to the dealer and take a brand new truck (not a 2014, a 2013) off the lot that has the same hvac system you have. See if it behaves the same way. If it does not, then ask service manager to take a look at why it is not the same. If they don't have a new one, try a used one off the same lot.

Anytime the dealer tells me something I complain about is normal, I get them to show me it being normal in other vehicles like mine.

Black2011 Enthusiast

Black2011

Posted
Posted

This is absolute bull. I have a 2011 and have had no issues, and occasionally I drive my truck at WOT for several minutes at a time. (10 or 15) with the a/c on. Now I cannot attest to whether or not the a/c is disabled, but you certainly should not feel warm or hot air circulating enough to heat you up.

 

If the dealer is not willing to address the issue, take it higher. Crappy service is just not acceptable.

  • 2 weeks later...
zedbear Enthusiast

zedbear

Posted
Posted

Funny, mine actually blows colder when I accelerate (not flooring it) but blows warm humid air sometimes when I'm coasting and cools poorly at idle. My 2000's AC was like a blast freezer at all times. I can also hear a slight whistle sound coming from the area of the control head on the dash that changes pitch with RPM......vacuum leak perhaps?

TJay74 Senior Enthusiast

TJay74

Posted
Posted

The AC clutch disengages once you reach a certain vacuum lever or throttle position, my 2010 kicks out under WOT and blows warm. Goes back to normal right after coming out of WOT and takes a couple of seconds to cool the vent air back down again.

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