Cascade Crew

91camaro_rs · Posted: Tue Aug 23, 2011 2:17 pm Post subject: heater stuck on defrost

idk what happened, but now my heater control is stuck on defrost, i can move the lever to all 4 settings but it only blows out the defrost vents and i took the face plate off and looked at it and the little vacuum thing turns when you move it, did a vacuum line fall off or something possibly?

iansane · Posted: Tue Aug 23, 2011 2:19 pm Post subject:

Vacuum feed line from the engine bay either fell off or cracked. Should be two that enter the firewall on the passenger side of the motor right behind the head. From there you can trace them to one of the canister/balls or the intake through a checkvalve T.

91camaro_rs · Posted: Tue Aug 23, 2011 2:23 pm Post subject:

alright sweet ill check that out

jchaussee · Member Joined: 14 Nov 2010 Posts: 1318 Location: renton

Did that solve your problem luke?

BluFbdy · Posted: Sat Aug 27, 2011 1:15 am Post subject:

hmmmm isnt there a door controlled by the vac lines? it could have fallen off under the dash maybe? but then again youd hear it

aaron_sK · Posted: Sat Aug 27, 2011 1:19 pm Post subject:

There are may doors controlled by vacuum lines under the dash. Wink

The way that system works is that vacuum comes from the engine bay through the firewall in a black plastic hardline that becomes purple at some point. It goes into a rotating disc in the HVAC control that is spun by the mode selection lever. That spinning of the disk causes it to shunt from the main vacuum feed to various lines under the dash.

All the vacuum controlled doors are spring loaded so they have "default" and "applied" positions. The default position for all doors in case of system failure is defrost only (the only one you need anyhow).

The common two places to have total vacuum loss (and therefore total system failure) is at the T where the system pulls vacuum from the engine (only rubber in the whole thing) and the selector disc which can get a gap in it and leak vacuum.