Questions and Answers

Cadillac Coupe Deville Heater Problem Q. Hi, The heat from the foot ducts is insanely HOT. The A/C does not work and air does not come out of the front vents. I was told to check the vacuum hose, or turn off the hot water to the cabin. I checked close to the firewall but couldn't find anything to turn off, or any vacuum hoses.

My question: Where can I find the "turn off" for the hot water, or the vacuum hose?? What do vacuum hoses look like? I have a Chiltons Manual, but I can't find info for my problem. The car is fun to drive but the heat is very bothersome. Hope you can point me in the right direction. Thanks for your time.

• 1980 Cadillac Coupe Deville
• 368 V-8 4-Barrel Carburetor
• Auto Transmission
• Either 78k or 178K miles

A. The heater control valve is usually located on the right rear corner of the intake manifold. There will be a heater hose going in and one going out to the firewall. This hose will be between ½" and ¾". There will also be a vacuum line about ¼" in diameter connected to it.

With the heater controls in the full HOT position, there should be vacuum at the line for the heater control valve. At full COLD, there should be no vacuum. If there is vacuum, there is a problem with Automatic Climate Control (ACC) module.

If there is no vacuum then the heater control valve is stuck in the open position and not shutting off coolant flow to the heater core. It's not uncommon for the heater control valve to go bad in this manner.