Defrost

[jdclemons]

Hi guys, i am having problems with my defrost. It will come on and blow, the heat works, blower works, but the gates that directs the flow doesnt. I cant figure out where the vacuum come from that works the gates. I have a 1987 Chevy Silverado EFI all original. Nothing has been swaped over, still have throttle body. If anyone can give me some pointers i will gladly appreciate it. Thanks. Heavy Chevy

[ToughBowtieTruck]

There is a vacuum line that is routed from the selector switch, through the firewall and to the engine's intake. Could be the vacuum line has a crack in it, or has been accidentally unhooked/blocked off if the emissions system has been modified at all (probably not from what you say). Not every truck has the exact same port for the intake. Most likely, behind the throttle body is where the line hooks up; usually there is a vacuum tree there where a few things are hooked together.

[jdclemons]

Thanks ill give it another shot tomorrow.

[mhicks]

There is a little piece of plastic that the arm connects to from the vacuum diaphram that is located in about the center of the deflector door. That little peice of plastic tends to break loose and will not operate the door properly. I ended up J B welding mine and have had no problem since.

[jdclemons]

Hey i replaced that plastic peace of one of my parts truck and is still having the same problem.

[jdclemons]

Hi guys, i found the line that goes through the fire wall broken and fixed it. The gates work now but i still have a slite problem. When i flip the switch over to defrost, the gate makes the air come out front and when it on anything else like max, norm, bi level ect.. the air comes out the defrost. any pointers.