Rear Defogger no longer works, press the button, relay clicks, but doesn't stay on. Fuses on that circuit are good. I understand this is a common problem with the HVAC control unit which is now a unobtanium part. Picked up a used one and it too has the same fault. Tested on the bench and the relay clicks and never stays energized, nor does the indicator illuminate and no power to the rear defog output pin on the module. Seems there is a timer chip on the rear defog module which controls the "on" time for the defog grid and that is the component that failed. Thought about bypassing the timer, but would have to keep holding the defog button to keep it on. I believe the timer is the 5977 chip in the attachment and that too is unobtanium. Any ideas for a workaround.
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