Question1978 Cadillac, El Dorado, 425. When I turn my heater on, the air-conditioner stays on, I put my hand behind the vents, I can feel the heat under the dash board, but only cold air comes out on all settings including on Defrost. The air coditioner compressor always comes on. I tried replacing all bad vacuum lines (I may have missed a couple). It all started when a vaulve (don't know the name, located in front of engine, a heater hose hooks to it and another goes to the block, with a vacuum line on the side) was leaking. I replaced that valve and now this is what happened.
Thanks,
Charlie
AnswerFIRST thing we need for you to understand is that when you put the DEFROSTERS ON the A/C compressor is designed to come ON as it helps clear the moisture from the windshield. This IS normal UNLESS someone changed the design.
The VALVE that was replaced was the HEATER FLOW CONTROL VALVE that allows engine coolant to be emitted into the heater core, thru the heater core and back to the engine via the other hose.
The vacuum hose that is attached to it, Should have NO VACUUM at this vacuum hose when the A/C is set to FULL HEAT. This is also true when your have it set for DEFROST.
When you put ON the A/C in the normal position, EXCEPT DEFROST there WILL be vacuum at this vacuum hose thus closing the flow of engine coolant thru the HEATER CORE.
You can visually see the valve open and close as you select from HEAT to A/C.
If you still have problems and have a camera that you can e-mail pictures of the valve that was REPLACED, I would like to see them.
E-mail them to me at:
meperganfortis@msn.com
As this website does NOT allow pictures.
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