Heating and AC question

[im2damncool]

The temperature control knob and the speed adjustment work fine but the selector switch doesn't. The one where you choose vent or floor or whatever. It will only blow out of the defroster no matter what setting you turn it to. I pulled the dash and found a red, white, blue and yellow set of wires coming from the back of the switch. (vaccum lines?)The yellow one goes to a silver cylinder right there behind the radio. But it had come disconnected. So I hooked it up and tried the system and IT WORKED!! Hooray right? Then once I tested all the selections I switched it to defroster again, to make sure that still worked. It did but when I went back to floor or vent or anything it just kept blowing out the defroster. I disconnected and reconnected that yellow wire but no go. What does all this mean? I'm baffled.

 

[hivolt5.0]

My guess is that the silver canister is bad. There is a flap inside the A/C - heater box the opens and shuts depending on which item you have selected: floor, defrost, A/C, etc. It all runs off of vacum, hence the multi-colored vacum lines you saw. If you look under the hood right above the A/C line going into the firewall you will see a black vacum hose. This hose runs runs to the selector switch which then redirects the vacum to operate the various flaps inside the A/C - heater box.

You must have a bad vacum valve some where in the system or vacum leak. That is my only suggestion. Perhaps someone else will chime in with more suggestions.

Good luck!

 

[trbkrb]

Yes, start checking all the vacuum lines under the hood and the dash for leaks. I've pulled the yellow line off before accidentally, and had a line crack under the hood, both resulted in defroster only. Most likely the vacuum solenoid on the defroster is not bad, it is just not getting enough vacuum to work. The defrost is the default setting. If you have a long rubber or plastic line, you can attach the solenoid directly to the vacuum tree on the firewall to test it, or use a vacuum pump.