Mechanics

HEATER

1992 Cadillac Deville • V8 FWD Automatic • 170,000 miles

1992 Cadillac Deville heater blows cold air. Replaced thermostat. Ran water thru heater core. Checked programmer arm operation. Having difficulty finding control valve. Been told its behind intake by firewall. Can you further describe where it is? Besides that valve, what else might solve this issue?


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Lemonade
November 24, 2010.



With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If they are.

The heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by an electric motor/actuator. The problem can be that the actuator is stripped or inoperative or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.

Wrenchtech
Nov 24, 2010.
Both hoses are cold. The actuator works and the blend door opens and closes. Still have no heat. I have learned that the heat control valve on this car is simply a tee without any vacuum or electrical control. Can such a non-mechanical device malfunction? Will replacing it help? What if I install a plumbing valve to restrict flow to the radiator and increase flow thru the heater core?

Tiny
Lemonade
Nov 25, 2010.
No, no, no. This car has no type of water valve. It is supposed to have hot coolant flowing through the heater core at all times and it controls the air flow inside. I would suspect that your heater core is restricted and likely will have to be replaced. You can try removing the heater hoses and back flush it with water pressure from the garden hose but it may not work.

Wrenchtech
Nov 25, 2010.
Removed the heater hoses and back flushed the heater core with pressure from the garden hose. Water flows freely thru the core. Could the core need replacing anyway? Does the BCM have anything to do with the heater? If so, where is it? How would I tell if it is malfunctioning? Thanks.

Tiny
Lemonade
Nov 26, 2010.
There is nothing electronic to blame if those hoses are not hot. That's what needs to be resolved now. Try connecting the hoses together and see if they get hot then.

Wrenchtech
Nov 26, 2010.
Finally connected the hoses together. They still do not get hot. This is very confusing.

Tiny
Lemonade
Nov 27, 2010.
Then you better see if the engine is getting hot. Is the upper radiator hose too hot to hold on to?

Follow the heater hoses back to where they connect on the engine and see if there is anything connected that could restrict them.

Wrenchtech
Nov 28, 2010.
Did this ever get resolved? Check that the heater hose coming out of the "T" is conneted to the LOWER input to the heater core. I had the same delemma and that was the problem.

Tiny
Twc265
Jan 9, 2012.