2019 Trail Boss - Defroster always blowing cold AC and windshield fogs up

wahoowad · August 30, 2021

Not sure if this has been going on the whole time I've owned it or what, but lately my defroster keeps fogging up my windshield any time I have the AC on.

I DO NOT have the defroster button selected, just the main vents. Seems like the defroster vent blows whether the AC is on or not. What's up with that?!?!

RCF71 · August 30, 2021

Seems to be a fairly common GM problem. My Camaro does it BAD! They have/had a TSB for it. I had it done (very involved, have to remove windshield) - no change! 74ish or lower and driving under 30mph, and it fogs up an area about the size of a basketball.

My Sierra does it if AC turned down to 70 or lower, and truck is sitting still. Not near as bad as my Camaro though, so it doesn’t bother me.

On the Camaro, they said it was due to some foam pieces on the defrost “door” to quieten the operation when it closes, but they kept it open too far. Supposedly they pulled those off when they performed the TSB, but I didn’t notice any change.