Help! HOT AIR!

[Elliott]

Just bought a 1979 Corvette and discovered when the engine is warmed up and driving at highway speeds the hot air just pours into the car from under the dash. Makes it nearly intolerable to drive. Sounds like there is a vacuum water valve under the hood that shuts water off when the heater doesn't call for it. We don't have vacuum to that valve so my mechanic is wondering if there is a control switch under the dash that may be bad? Don't have a parts manual yet, but have one ordered. I've read where some owners with cars that do not have a/c resort to in-line shut-off valves and have had good luck minimizing or eliminating the problem. Mine has a/c, but am also considering the shut-off valve option. I also realize that I may have a damper malfunctioning under the dash, but am not thrilled about tearing into it. Our concern is whether installing shut-off valves may not totally solve the problem if there is some residual heat that may still come through the ducts. So before we tear into the dash, I'm wondering if anyone has had experience with this problem. TX

 

[L82 Shark]

Elliott, my 1979 has the same problem but already has the inline shut off installed under the car so it doesn't show and it takes care of the problem. I turn it off at the beginning of the warm season and open it back up in the Fall.

I have talked to my brother who owns a corvette repair shop and he say more than likely the heater control cable needs to be adjusted. The cable stretches and distorts after years of use. Of coarse you have to disassemble the center console and part of the dash to get to it.

VALVE WORKS GREAT AND IS EASY otfl

Hope this helps

 

[RMS73]

After seven years of searching for my car's hot air issue I found the seal between the firewall and the fender on the passenger side was broken. This allowed the hot engine compartment air to feed into the plenum by the passenger pick panel and up into the HVAC blower fan and into the duct work.
Roger

 

[Elliott]

L82 Shark, Thanks for the info. I had discussed with my mechanic yesterday the option of the shut-off valve and when I picked up the car today he had gone ahead and installed one as a temporary fix waiting to hear what I found out from this site. Again, we aren't real wild about tearing into the dash, etc. Anyway, I took it out tonight and it solved the problem. The issue will be this fall because if I open the valve it is going to provide way, way too much heat. It will be all or nothing, I think, unless I can control the amount of heat with the valve. Will have to see, but for now it's fixed. I appreciate the info about the cable because that tells us where to look next if I want to fix it permanently. I may have to remove the center console anyway because I have electric windows and the driver's side switch contacts are probably worn because I really have to push hard to make contact and the console limits the movement of the switch to where sometimes I can't close the window. Always something I am learning, but at least if we remove the console we can take care of a couple problems at the same time. Thanks again for your help!

 

[Elliott]

Roger, thanks for the information. I think we have it temporarily fixed and fortunately we didn't have to spend the time and energy you did in order to find the problem. It is good to know, though, because that can't be the only time a seal has failed. TX Dave

 

[RMS73]

To adjust the heater core diverter valve only the passenger side dash panel needs to be removed. The diverter valve control control is attached to the valve on top of the air box in front of the passenger.

Roger

 

[Elliott]

Thanks, that wiill be helpful because eventually I think we will need to permanently fix it beyond the temporary fix we have for now. I appreciate the information! Dave

 

[Vettehead Mikey]

The heater shut off valve should make only a minor difference, many Corvettes were not equipped with one from the factory (like mine) and work just fine. If you've got that much heat pouring in, there's an issue with the ducting under the dash.

 

[Elliott]

The valve made a big difference, but I think you are probably right and that we will need to check the linkage and dampers. TX Dave