i'm having issues with my 1980 cadillac coupe deville. when i first start the car the heat warms up and stays warm but as soon as i turn the car off or mess with the temp settings it gets cold(or whatever the temp is outside) and wont heat up again until i let it sit over night and start the process over again. ive replaced the heater control valve and that didnt do it. next step im going to try will be to replace the heater core but im looking to see if im headed in the right direction. guidance?

thanks

 

It could be your in car sensor which affects the temp. setting. Your ECC programmer has a diagnostic lead, it is black and white. You will find it on the back of the programmer. Does you dash display come up with any codes?? Before you go and blow a bunch of money get the diagnostics done and then you know where you are heading. These electrical gremlins will drive you crazy.
Good luck.

 

no i dont get any codes on the dash. where is the ecc programmer located? thanks for all the replies, it seems like its just you and I in this forum.

 

The ECC Programmer should be about center under the instrument panel on AC module. There will be various vacuum lines running from it, so check all of these for leaks, cracks,etc. The diagnostic lead is black/white.I have about 12 trouble tree diagnostic charts. If I knew exactly what and when things were happening maybe I could send the right information to help narrow things down a bit.This is a very complex system and involves circuits that you would never think had anything to do with the heater function, so, guess work is definately out.