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73-87 Chevy _ GMC Trucks => Interior & Equipment => Heating, Ventilation & Air Conditioning (HVAC) => Topic started by: m3talc0re on December 17, 2016, 09:14:28 pm
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I've noticed that running my defroster doesn't do anything... I mean, it still blows heat, but it's trying to go to the vents facing the passengers. It doesn't seem to switch to the defroster. Any ideas?
This is on an 83 GMC Sierra Classic btw.
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so you dont heat the blender door move when you move the selector from vent to defrost?
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I don't think so. I've tried to listen for that and I didn't hear anything.
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If you don't hear the faint hiss of the vacuum pod / solenoids when you change selector positions, then you don't have a vacuum signal to move the blend door that directs the air to the different outlets in your cab. Often, the vacuum line from the engine compartment has been disconnected at the firewall (engine side) or at the vacuum source itself (engine). Check to see that it is connected. If your truck is similar to mine (85 Silverado), the port will be found on the firewall just left of dead center (as you look at it standing in front of it). Have you performed any work recently under the hood or under the dash that might have accidentally disconnected a hose?
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Not really, but I'll go looking for it in a minute while I'm messing with the alternator. Thanks!
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Where is it supposed to be connected at on the engine?
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There is usually a round vacuum canister over near the A/C plenum under the hood.
One port on the canister has a vacuum line running to the engine vacuum fitting on the back of the intake manifold, and the other port on the canister is where the vacuum line from the heater connects. The canister keeps a vacuum reserve that is high enough to run the heater's vacuum motors even under full acceleration when engine vacuum goes low.
Bruce
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That did it. It was a little black and gray tube, connected it into the little clear bend coming out of that round vacuum canister, which still had the rest of the broken off piece of hose in it. I heard the little vacuum noise and it changed over to the defroster :D
Thanks! XD