Why do my vents change where the air blows when the engine is loaded?

[Steamroller]

I have a 2001 ACR. Let's say I have the A/C on, and it is blowing out of the three dash vents directly above the radio. Whenever the engine is notably loaded, the air stops blowing out of the three dash vents and starts coming out of the windshield defroster vents. The air will resume blowing out of the three dash vents when I let off the gas pedal.

Any thoughts? Is the vent selector actuator in the HVAC system vacuum-actuated, so when the engine is loaded there is not sufficient vacuum to keep the vent selector in the appropriate position?

 

[Qualitywires.com]

It's normal...when the car is accelerating, it shuts off the A/C for less load on the car and puts it's all in the engine. I think it's kind of cool! Kinda of like in Star Trek when they fire the phasers..or the proton whatever bomb, they have to divert all the energy to the weapon...heh! I'm a geek!

 

[Fast Freddy]

my 2001 acr does the same thing. so are you saying this prevents you from blowing up your ac compressor at max rpm's. if so that is a cool feature (pun intended, lol). i have blown several AC compressors in gm vehicles because the AC compressors do not like high revs.

 

[Steamroller]

I am aware that the A/C shuts off under notable engine load, but I am curious why the air flowing out of the three dash vents switches to the windshield defroster vents.

 

[PBJ]

The reason is in the one way check valve behind the radio. Replace the valve with a check valve from a Dakota and it will not do it any more. At wide open throttle the vacuum drops to zero or near that and vacuum is what keeps the blend door in the position for the vents...defrost is the default position. The Dakota valve is a little bigger but it solves that problem. Just pull the radio and behind the a/c head on the tunnel the is a small black valve in line to the a/c controller...that is what you need to switch. Make sure you install it in the right direction...just as you removed the old one. The vacuum can only go through the valve one way.
Later,
Joe

 

[Qualitywires.com]

it diverts it to the windshield to give you a crisper view of the road when accelerating.


Not really...heh! I 'm not sure why it would go to your window instead? I never heard of that one before? You sure it's not warm air blowing up there hitting the cold windshield and just causing condensation?

 

[Hisserman]

Great post, Joe. Thanks.

 

[Steamroller]

PBJ,

Thanks for the help. Just as I suspected... vacuum-related. Does the Dakota check-valve simply further reduce the amount of flow back through the valve? I would think that if it sealed "perfectly" in one direction, then when you wanted to actually change the air flow from the three dash vents to the windshield defroster vents, it would not allow the transition to work correctly. I am very curious... will you please offer some additional detail?

Thanks again for your help!

 

[PBJ]

Steamroller,
The Dakota valve actually is a larger piece with a cannister made on to the valve...sort of like a vacuum reservoir. When you go to WOT, it has a small amount to keep the doors in the position that you select. It is still a one way valve like the factory piece..no change. The a/c head is vacuum operated for the evaporator housing doors and the mode door that changes positions for outlet needs vacuum to hold it in place. When you change positions it bleeds the vacuum off to allow the door to move. I think that is what you were asking...I hope that helps.
Later,
Joe
P.s. I can get the part number of the revised valve if you need it. It was a TSB revised part for the Dakotas and BR trucks for the same problem you are having.

 

[Cop Magnet]

PBJ you sound like the man to answer our thermostat problems! How about it, any fixes on that useless center knob that does nothing to control the air temp coming out of any vent? You'd think after two generations of a car they could figure this out at the factory...