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Old 08-16-2014, 07:31 PM   #1
Ralph50
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Join Date: Apr 2008
Location: Mt Clemens, Michigan
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Heater-vent problems

2000 Jimmy - 114K - 4WD - The heater was blowing air out of the vents all the time. Also noticed that the vent door that pulls air from inside was always open except in one position on AC.
I dissasmembled the heater control that changes the direction of the air and found that there is a rubber seal or diverter that is approx 1 1/4 inch in dia and has grooves in it where it opens and closes the air ports depending on what the selector is set to. This rubber was swelled and was larger than it should be because it did not fit the steel plate behind it. I bought a new head unit for 66 dollars and it solved the issue.
In addition to this problem I found that the vacuum hose was completely falling apart. I ran new steel 3/16 brake lines all the way back to the 4WD area. Some one on the internet said that when oil leaks in the 4WD unit it is pulled up and eventually gets into the heater control head. I think this caused the rubber diverter to swell.
To fix this I made a small vacuum canister from 1 1/2 PVC tube, 3/16 brake line and JB weld. I put this in front of the vacuum line that feeds the heater unit, (its a small black plastic 1/8 inch and goes into the wire harness and then feeds up to the heater control head), now I am sure there will not be any oil going to the heater head, the canister will trap any oil. I may have to empty it once in a while but better than a new head unit.
Also had to clean out the small check valve because it had junk inside and was not working, used soap and finally blew air in and it fixed it.
Ideally when the car is shut off the system should retain the vacuum in the canister.
Oh the vehicle vacuum canister is located behind a bracket that holds the anti lock brake unit. The canister body is actually in the fender area but the nipple faces the engine. I looked forever finally found it, its there just keep looking with a small mirror.
All back together working good, 4WD working ok.
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