I was going for a ride last night in my 1979 Delta 88 Royale two door coupe and the heater went from blowing hot air to cold. If I have the heater off and have the air temp on hot, hot air comes into the car. But as soon as I select heater and turn the fan on it goes from hot to cool. Any help as to why this is happening would be appreciated.

 

You've got a loose air temperature flapper door - it's blowing closed when you put the fan on.

Others (or your Chassis Service Manual) can tell you exactly where the cable (or vacuum pot) and lever are for the door, but they are generally up behind the middle of the dash or the glove compartment.

- Eric

 

Maybe low on coolant?

 

Thanks for the help!

 

So you figured it out?
What was it?

 

Do you have the Temptronic automatic climate control or not? If not, then the problem is a common one. The 1977-1990 B/C-body cars like yours (and the 1978-88 A/G-body cars, which use the same design) have a cable-actuated heater blend door with a plastic actuating bellcrank that usually breaks. Remove the glovebox liner and you'll see the bellcrank and the cable end. Replacement bellcranks are no longer available, so if this is the problem you'll need to repair your old one with epoxy and reinforcements.

If you do have Temptronic, the problem is likely the programmer unit also located behind the glovebox.

 

No, I haven't fixed it yet but if I get a chance I'll take out the glove box insert and take a look at the cable-actuated heater blend door and see if the bellcrank is the problem. Eric and Joe thanks for the help, I had no idea where to even start.