Vents turn off when getting into boost...

Seems like whenever I have the vents on (especially the A/C) and I get into boost, they stop blowing air until I let off the gas and start pulling vacuum again. I know this has to be a check valve but I don't have really any time to track it down. It's really annoying because it will also blow air through the defroster sometimes. Any help would be appreciated. Thanks.

At full throttle the A/C compressor stops, but the fan should still blow air.

sounds like you have a pretty good vacuum leak somewhere. im not sure but iwhen the vents stop, the blower is still running, but with no vaccum i think it defaults to the floor or defrost vents. just start checking all the hardlines on the firewall for cracks.

It is going to the defrost. That is where EVERY car defaults too. You are losing vacuum to your bulkhead. There is a one way check valve that is broken allowing the vacuum to release from there. It is on the firewall and looks like a small pancake in a vacuum line. OR YOUR CONTROL HEAD is bad.

To chcek it, get a vacuum pump ($20 bux or so) and pump it up while using the control head. You should be able to pump it up and hold it while changing the selector from panel to defrost. If not, you need a new head.

That one way check valve is lie $.20. Yes thats twenty cents.

Chris

Where is that one way checkvalve though? Passenger side?

I know there is a WOT relay for the A/C but that isn't it. I was only at partial throttle (but in boost) and I noticed the vents completely stopped blowing. Sometimes air will blow through the defrost though when I hit boost. I can see the windshield fog up at night when it happens.

I have a vacuum pump so I'll check for the control head thingie.

Your best bet would be to look at an EVTM. I do not know but if you dont have an EVTM, you could ALWAYS follow the vacuum through the firewall.

Chris

Start at the vacuum tree located about the middle of the wiper cowling, underside. Trace all the hard lines back from it. I think you'll find one of them broken. Easy fix, just use a rubber vacuum line with an id a bit smaller than the od of the hard line. Push the hard lines into the rubber line. Use a daub of sealant on each end if you think you need it. I had the same problem a while back and one of the hard lines was broken.

Or...spend the thirty cents and do it right.

Chris