I was wondering if you would be so kind as to help me out with offering me some advice. I have a 1987, C4 corvette. I am not getting any heat when the fan is on and the heat is on. I am sure that I am not getting vacuum to the heater control valve. I have torn the dash apart and traced the vacuum lines that apply. There is a vacuum line that runs from under the hood, through the firewall to an electronically controlled module of some type where it meets with many other hoses, one of which is the hose which runs back to the heater control valve under the hood. This electroniccontrol station or module appears to be controlled/connected to the main heater a/c control unit in the center of the dash. Do you have any suggestion as to why the heater a/c control unit is not effectively executing the command to distribute vacuum where necessary? Oh yeah, another hose which is common to this ecm/vacuum manifold is one which opens and closes the windshield defroster vent damper. I would really appreciate your thoughts and advice. Thank you very much,
Zack Clark
(707) 332-3419

*when manually opened, hot water does flow through the heater core via the heater control valve
*Iknow the damper opens and closes which controls air flow between heater core and recirc. air

 

Hope ya don't mind that I moved your thread......
You should get some good responces here in the C4 forum.

 

Sounds like your car has Automatic Temp. Control. Do you have a digital readout or a slide bar that has temp. settings? If it does, more than likely your a/c programmer is bad. It has 3 vacuum servos in it and the temp control servo is bad. Unfortunately, the only fix is to replace the programmer. Just make sure you have a good vacuum source of at least 18" of vacuum.

 

Hey, fizzfueler, I have the same problem with my 87. The air flow changes from heat to defrost to the dash in A/C but the vacuum valve in the heater line does not operate. Also, I tried holding my open manually, and I still didn't get any hot air. If you find the problem please notify me via e-mail at bhanback@tds.net. If I find the answer, I'll do likewise. Thanks. Catman

 

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