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Climate control vent selection

SurplusFan98

NAXJA Forum User
Location
LA
Hi all

I have the classic "air only blows from the defrost" issue, but none of the common things seem to be the issue. Fan blows strong, AC works and blows cold, but only from the defrost vent.

I have eliminated ALL vacuum leaks under the hood. Confirmed with a vacuum gauge that my leak is definitely coming from inside the cabin. Main lines pull 20psi and hold it in the canister when pinched, but steadily lose vacuum when the little line into the firewall is in circuit.

I went in the cab and pulled a vacuum on ALL the lines in the vacuum connection point behind glove box. Everything holds vacuum, and when I put the gauge on the black line at that point, its the same 20psi as under the hood. I then made a little jumper vacuum line and went from the black source line to each of the other lines, and I could sort of hear most of those working (couldn't see them because I was by myself and thats a 2 man job).

I'm pretty confident that I have isolated the vent selector switch. But, I don't know how to test it, and I don't know where to get one if I found that it was bad (looks like used on ebay is all thats left). Is there a way to test and/or fix this component?
 
Sounds like the switch is leaking. Replacement with a used part is probably the easiest solution (ebay, junkyard, etc). You could try to find the leak by pressurizing it and spraying soapy water (or use a smoke machine if you have one), and then epoxying the leak, but that thing is small and intricate enough that it might be challenging.
 
Sounds like the switch is leaking. Replacement with a used part is probably the easiest solution (ebay, junkyard, etc). You could try to find the leak by pressurizing it and spraying soapy water (or use a smoke machine if you have one), and then epoxying the leak, but that thing is small and intricate enough that it might be challenging.

I actually did try to use a smoke machine from the connection under the hood, but my smoke machine is manually pumped and I can't be outside pumping and inside looking. I tried to pump fast and look inside for smoke, but I never saw any.

The switch on the inside is just a metal plate on 1 side with rubber canals for air travel on the other. The airways themselves are VERY small. Wonder if there's a way to grease/shim that plate so that it seals up. I'm sure the rubber has just shrunken over time...
 
The switch on the inside is just a metal plate on 1 side with rubber canals for air travel on the other. The airways themselves are VERY small. Wonder if there's a way to grease/shim that plate so that it seals up. I'm sure the rubber has just shrunken over time...

So that WORKED!

I pulled the switch apart and cleaned the old grease off of the rubber disk with some brake clean. I sprayed brake clean down inside the little holes on the plastic side of the switch. My guess is that just the cleaning is what fixed it. I imagine that the old grease just shifted over time with how hot it gets down here in the South and clogged the holes and rubber canals up. However, I did also VERY lightly apply some dielectric grease to the raised parts of the rubber disk hoping that would help them seal. It probably didn't, but I don't care as long as it works!

Man, trying to solve that issue was a chore!
 
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