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Defroster Dilemma


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I'm experiencing problems with my defroster/entire climate control system. I own an 89 GL wagon with AC. The problem occurs frequently when the outside temperature dips into the chilly range (40 degrees farenheight or lower). When I rev the engine to 2500 or above, the heater will stop blowing air from the defroster and switch to the panel vents. This also occurs if the system is set to "heat" or "bilevel". When engine rpm drops below the 2500 range the system will return to its previously set state. This has been driving me crazy!!! I have a hunch the problem is related to the vacuum system. I would greatly appreciate any help!! Thanks!!!

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Because, at higher RPM/wide open throttle the engine produces very little vacuum. So, once the vacuum in the little plastic vacuum reservoir is depleted all of your vacuum operated solenoids and doors return to their neutral or springloaded positions. Once the throttle begins to close and starts producing vacuum again the solenoids and doors return to the positions indicated by the control knobs. If it happens almost immediately you probably have a vacuum leak somewhere in the system. If it takes a few minutes it's probably normal operation. I have a long hill on my daily drive and mine do it about 2/3s of the way up the hill every day. It's kind of annoying, but I haven't had time to look and see if I might have a small leak somewhere, besides I suspect it's just the way the system works.

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Another vote for a slow vacuum leak somewhere in the system. Vacuum from the little canister to the heater controls should be staying relatively constant, regardless of engine load, and even with the engine off.

 

A handheld vacuum pump and vacuum gauge will help troubleshoot and find leaks quickly. I picked one up a few months ago for $25, and it just helped me figure out why the heater controls weren't working on the Hornet. It turned out that the hoses going to the vacuum canister were hooked up backwards, and there was no vacuum getting to the controls at all.

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Thanks guys!! I picked up a new canister at the pick a part today from a wrecked 93 loyal (along with a new headlamp lens!! Love that junk yard!). I pulled off the hose and it made a satisfying whoosh! Climate system works great now!!

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Hmmm....I'll have to try that on mine. It's always had a little bit of that problem, which has been caused by vacuum leaks in the supply for the heater controls. Last winter, it got bad enough that I had to stop and get out in Kluane Village at 30 or 40 below and eliminate some of the vacuum fittings so it would at least make the heat come out of the defrost when I was driving on flat ground. That sucked.

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