86 gmc Defroster problem??

[Scott26]

My defroster is not working.The Heater works good, but when i switch to defrost it still only comes out of the vents. I can manualy move the door by the lever and it will work.I dont know if im missing something or something with the vacuum but i cant get back to see with out taking my whole dash apart why its not opening by itself.

[old Rusty C10]

if you have a non ac truck its run by cables not vacuum otherwise you need to chase down vacuum lines

[Scott26]

thank you

[77gmcjoe]

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.

[motornut]

the one by the pedal is for floor to defrost,
the other is to vents or not

[motornut]

you can remove the air tube part in front of the glove box fairly ez
when the white piece breaks the vents wont turn off
in this pic mine is broken

[87chevy.com]

you can check to see if that pod thing is broken with a vaccum gauge... if you hook up a mityvac to it and pull vacuum and turn your vents on... if it doesnt actuate, its not a good pod. if it works you have a vacuum problem.
clint

[Scott26]

thank you helped alot!

[72freak]

I had the same problem. It was the small hard plastic vacuum line coming out bu the heater box with some electrical wires. Hooked it to a vacuum source and all is well.