A/C vent issues

[johnson350]

Whenever I switch the climate control lever to Max a/c it will take it a few minutes for the vents to change from defrost/floor to blowing straight out. This is the only way I can get anything blowing out of the front vents now. Whenever I step on the gas from a dead stop the vents change back to defrost/floor, and then they'll switch back after a few minutes of driving. It used to take a while whenever i switched it over to vent, except now it won't even move when vent is selected, it just stays on defrost/floor vents. All I know is that the vent doors under the dash are vacuum operated. Im not too familiar with this setup and have no idea where I should start? :?

 

[CWPottenger]

You are loosing vacuum for sure and have a leak somewhere.

I would start with the vacuum tank and the vacuum lines/fitting to and from. After that the multi port vacuum connector on the back of the HVAC control panel can leak or come loose. If not those then it is a piece by piece hunt.

 

[johnson350]

OK, thats exactly what i did. I checked under the hood and had good vacuum going to and from the tank. So I pulled out the radio and glove box and all the vacuum lines were like brand new, still flexible. It turned out to be the selector switch leaking. I actually took apart the switch and bent the little metal tab so it tightened it a little bit, then put a lil grease on it and reassembled. The bad news is I broke one of the plastic tabs that holds the whole thing together (barely staying together). It works for now but will have to eventually get a new one.

Reinstalled and now every vent moves nice and quick.

 

[wrenchbend1]

Johnson ,
Defrost is the "default" Mode for the entire system should it lose vacuum. This allows the car to be driven and be able to clear windows without engine vacuum.It is designed that way by General motors . There should be a vacuum check valve before the vacuum reservoir that holds vacuum in the reservoir when ever you step on the gas and diminish engine vacuum . this is why the modes change when you accelerate and when you level off the modes change back. hope this helps you understand the how and why. start under hood and find your vacuum line to your heater/ac system and start there .

Whenever I switch the climate control lever to Max a/c it will take it a few minutes for the vents to change from defrost/floor to blowing straight out. This is the only way I can get anything blowing out of the front vents now. Whenever I step on the gas from a dead stop the vents change back to defrost/floor, and then they'll switch back after a few minutes of driving. It used to take a while whenever i switched it over to vent, except now it won't even move when vent is selected, it just stays on defrost/floor vents. All I know is that the vent doors under the dash are vacuum operated. Im not too familiar with this setup and have no idea where I should start? :?

 

[johnson350]

Ok, so the problem ended up being in the rotary vacuum switch behind the dash. I replaced it and it blows out the front once again. I was also sure to spray some white lithium grease on the moving parts because it was a little stiff, this got it working smoothly again.