Posted: Wed Dec 12, 2012 2:00 am Post subject: Rear window Defogger
Doe sanyone know the voltages that are suppose to be present on each pin of the Rear window Defogger relay. I have an inop rear window defogger on a 2004 impala base.
What my testing revealed. I picked up a scrap yard HVAC control unit and it tested exactly the same as my original one. With eithe runit installed the defogger is inoperative and there is no click from the relay when the button is switched on or off.
Pin L3 had 12.64v key on engine off
Pin N2 No voltage as it is supplied by the relay
Pin N3 .563v with key on engine off defogger button off
Pin N3 .028v with key on engine off defogger button on
Pin L2 No voltage present with defogger button on or off
The car has a Brand new factory BCM that I thought may have been part of the issue as it had several other issues going on with the car. Everything except the rear defogger was fixed with the new BCM.
Thx in advance for any help anyone can provide. I am thinking I need to order a replacement HVAC controll unit.
The rear window is fine. I think the issue may be with the HVAC controls as the Relay is not clicking at all. The power comes from the BCM and withthe engine runnign the voltage from the BCM goes to alt output and the ground circuit looking at the wiring diagram is completed thru the HVAC control unit. When I run a continuity test for ground it shows all zeros but I do nto get a buzzer on the Multi meter. when I turn off the Deffoger switch it shows as an open circuit. So I am almost sure the issue is in the HVAC control itself.
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