Hello everyone,

I believe this is my first post.. woohoo!

I have searched the forums extensively and always found a dead end when it came to this particular issue.

Heat in the car worked well up until a couple days ago.

The vacuum line to the heater control valve under the hood appears to be pulling vacuum 100% of the time, bypassing the heater core and thus leaving me without heat. Heater core is new, the control valve is new, HVAC controls and blend doors all work properly. I did find a vacuum diagram of an IROC somewhere on thirdgen and it shows a diverter valve switch on the vac line to the control valve.

My theory is that this valve got stuck open somehow as the HVAC is in the max cool position/AC.

My questions are;

Where is this valve switch located?
What does it look like?
How to fix this?

​​​​​​To be clear, I know for a fact that this is vacuum related as the heat works perfectly when I disconnect the vac line from the heater control valve. The heater core is PERFECTLY FINE.

Cheers everyone.. hope we can figure this out.

- otherthrakker

 

I believe this vacuum is coming from the vacuum switch on the HVAC control panel. It's actually a rotary valve that gets spun by the sliding switch that controls what function you select... Heat, defrost, cool, etc. These tend to break.

The fix is simple... Drill out the center and use a simple nut and bolt with locktite to secure... There should be some posts that show how to do it... Search hvac vacuum switch. You will have to pull the console panel out....