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HVAC air flow is on half through the floorboard and half through the defrost ducts

Tiny
COVERLAND
  • MEMBER
  • 1992 PONTIAC GRAND PRIX
  • 80,000 MILES
I have the car listed above 3.1 with a heater/AC problem. Fans work great, the hot/cold lever seems to change the blowing air from cool to warm, and the air output is split between the defrost and floorboard. It doesn't matter which switch I depress (AC, defrost, vent, floor, etc), the air flow doesn't change. Seemingly half through the floorboard and half through the defrost ducts. Even the fans speeds work fine. A couple of knowledgeable guys have told me they think the problem is in the 'blend back door actuator' but I haven't been able to find any instructions anywhere on how best to change this component and I had to wonder too, if there isn't some way to just run the AC compressor directly to the battery through a fused switch versus tearing into my dash when I'm not entirely sure what I'm looking for. Anyone have any experience changing one of these components?
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Saturday, May 4th, 2013 AT 12:26 AM

9 Replies

Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
The AC programer controls that door. Remove the glove box liner you will see the linkage hooked to a arm that is the programer.
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Saturday, May 4th, 2013 AT 1:06 AM
Tiny
COVERLAND
  • MEMBER
  • 32 POSTS
So that's to say you think the problem may be with the AC programer?
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Saturday, May 4th, 2013 AT 9:21 AM
Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
After reading through your question again. Your problem is a vacuum leak somewhere usually under the hood. You will need to check for any cracked vacuum hoses or leaks. I used to use a can of brake cleaner to spray on the vacuum hoses down. When you spray on the leaking hose or component the engine idle will pick up RPM's. Then you will and just need to repair the leak and the AC will come out the vents properly.
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Saturday, May 4th, 2013 AT 11:13 PM
Tiny
COVERLAND
  • MEMBER
  • 32 POSTS
Thanks, I'll check for a vacuum leak today. I haven't checked to see if pressing the AC switch actually turns on the AC compressor when the engine is running and am guessing that if it were a vacuum leak, that wouldn't stop the compressor from running when the AC button is pressed. Thoughts on that?
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Sunday, May 5th, 2013 AT 4:59 AM
Tiny
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  • MECHANIC
  • 3,544 POSTS
It should still turn the compressor on.
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Sunday, May 5th, 2013 AT 9:25 PM
Tiny
COVERLAND
  • MEMBER
  • 32 POSTS
Is there some low Freon protective switch that prevents the compressor from coming on if the Freon is low? If there's a low Freon type switch that keeps the compressor from turning on though, how in the heck to they get it to charge back up.

I was wondering if there might not be two issues going on. One, the vacuum leak (or blend back actuator), whatever it is; and then the low Freon issue that may be keeping the compressor from turning on.

Kind of a frustrating deal but I'm not inclined to give up because the AC used to work great in this car.
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Monday, May 6th, 2013 AT 6:03 AM
Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
When you push the pin in on the valve does any Freon come out?You may have a leak somewhere. You can buy Freon with a gauge at the parts store. It's not that expensive. You hook into the low side valve. The two valves are different sizes so don't worry about hooking it to the wrong one. It has a red and green scale to make it easy on you. The gauge should only reading 30 pounds anything under that it is low anything over that it is over full.
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Monday, May 6th, 2013 AT 4:19 PM
Tiny
COVERLAND
  • MEMBER
  • 32 POSTS
And you can charge it without the compressor running? (I haven't done an AC charge before)
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Monday, May 6th, 2013 AT 5:58 PM
Tiny
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  • MECHANIC
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Yes, but it needs to be under 30 pounds on the gauge.
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Monday, May 6th, 2013 AT 6:04 PM

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