Cadillac Repair: No Heat in my Cadi, heater control valve, heater cores

Question
I have a 1991 Cadillac Deville 4.9
Last week when it dropped below 20 degrees outside I lost my heat. I've had the system flushed. heater cores free of obstructions. I've disconnected the Heater control valve, the Inlet hose is HOT , the valve is a three-way , the return is not hot eventhough I can blow threw and get antifreeze through the heater core. I've also checked and found the heaters blend-air door is working fine...anything you can tell me ?

Answer
If you have coolant flow thru the heater core your problem has to be with the programmer that opens and closes the heater damper door. Are you positive that the heater damper door is opening all the way ?.

Did you physically inspect the programmer to see that it is opening the damper door ?.

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