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77gmcjoe · 11-14-2010, 09:30 AM

I've had trouble with the defroster in a couple of squarebodies and it always ended up being a bad vacuum pot or rotted hose inside the heater/ac plenum. It's a pot on the top of the plenum that opens the door to move the air upwards. It's kind of a pain to pull things apart to get to them, but I'd bet that's your problem too.

11-14-2010, 09:30 AM	#4
77gmcjoe What do we get for $10? Join Date: Oct 2004 Location: Beardstown, Illinois Posts: 340	Re: 86 gmc Defroster problem?? I've had trouble with the defroster in a couple of squarebodies and it always ended up being a bad vacuum pot or rotted hose inside the heater/ac plenum. It's a pot on the top of the plenum that opens the door to move the air upwards. It's kind of a pain to pull things apart to get to them, but I'd bet that's your problem too. __________________ 1977 GMC K25 400/400/205 1989 Chevy Suburban R1500 350/700R4 (work beater) 1994 Chevy K3500 dually 454/4L80 1996 Corvette LT4 350/ZF 6 speed 2000 Bonneville SSEI Supercharged 3.8 Liter V6 1966 Chevelle 2 door sedan (Needs major repair )