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I have been battling this issue for about 3 weeks now. When the car goes into boost, the air coming from face vents shuts off. I’ve trouble shot the following,
1. New water **** that holds vacuum
2. verified all hoses in front of vacuum reservoir are tight
3. If i actuate the pump using Cruise control, it wont shut off after 30 seconds.
4. I removed all front hoses and plugged all the nipples and it shuts off after 5 seconds, so pressure gauge works.
5. Used a mityvac to pull a vacuum and all porta held a vacuum except the line going to Plenum
Is that symptomatic of the check valve failing?
Im considering placing a check valve in-line from the manifold feed.
Do you hear any funny noises under the dash? Like a rattle or buzzing when you change the AC/heater controls? If so you may have a bad vacuum solenoid under the dash. The solenoids that run the AC/heater system use engine vacuum and solenoids to control it, and if you have a bad solenoid, the system defaults to defrost with heat. 20 years ago my 85T did the same thing, stopped blowing out the vents and instead shooting heat out the defrosters only while under boost. Re-ran all the vacuum hoses and ensured all under the dash was good and the issue went away.
You issue still appears to be a vacuum issue as the only connection between the engine and AC heater system controls is the vacuum.
Attached is all the info I have on the Z31 vacuum system
Do you hear any funny noises under the dash? Like a rattle or buzzing when you change the AC/heater controls? If so you may have a bad vacuum solenoid under the dash. The solenoids that run the AC/heater system use engine vacuum and solenoids to control it, and if you have a bad solenoid, the system defaults to defrost with heat. 20 years ago my 85T did the same thing, stopped blowing out the vents and instead shooting heat out the defrosters only while under boost. Re-ran all the vacuum hoses and ensured all under the dash was good and the issue went away.
You issue still appears to be a vacuum issue as the only connection between the engine and AC heater system controls is the vacuum.
Attached is all the info I have on the Z31 vacuum system
Thank you for the reply. I have figured it out. The check valve on the intake manifold side has stopped working allowing boost to deplete the vacuum. I’ve added an external checkvalve in line with the plenum supply and it has fixed my issue. Thank you for the images, however my vacuum canister is different. My hose with the “m” for manifold is closest to cabin.
Thank you,
sal a
