I do have fond memories of working on ’78 Caddies in my younger days. The reasons for no heat on this vehicle are numerous. First of all, the most common is the hot water valve that is under the hood. How you check this is to feel the heater hoses in and out of the heater core. Both hoses should be hot; if one is hot and the other is cold, you can suspect the valve or a blocked core. Next, and the most miserable of all is the programmer assembly, which is located against the firewall in the car under the glove box. This electronic device sets the temperature and where the air is delivered. They were a nightmare then, and I am sure they still are today. The best case of all would be if you have a broken vacuum hose under the hood that feeds the HVAC system. The hose should come from a canister, which looks very much like a quart can we used to get grapefruit juice at the grocery store so many years ago. This canister should have an engine vacuum hose going to it, and a hose coming out that feeds the HVAC system. These cans would typically rot out and would not send vacuum to the HVAC assembly. Best of luck restoring this beauty.
Car Care Tip:
Whenever your car goes to a shop and you know it will be on a lift, it’s a good idea to ask the shop to give the wheels a spin. You don’t want to have a car with hanging-up brakes, this will cause a handling problem and a waste of fuel. Your vehicle has to work that much harder when the brakes are dragging.
Larry Rubenstein is a master technician who owns a North Shore service station. His column appears every Saturday. Write to Larry at the Salem News, c/o Auto Scanner, 32 Dunham Road, Beverly, MA 01915, or send an email to firstname.lastname@example.org.