vacuum switching in '74 temp control unit with A/C

[John House]

Anyone know how the vacuum switching in the temperature control unit is supposed to work on a '74 C20 with A/C? Problem I have is that there are two vacuum-operated doors, one under the cowl vent outside the cab on the passenger side, and one in the passenger kick panel area, and they are both connected to the same vacuum line coming off the manifold attached to the temperature control unit, which tells me they both open together, but there are no temp control unit positions that open those doors, and in fact in the A/C, Heater, and Defrost positions, all vacuum in the canister bleeds off to the atmosphere (tested manually). So I assume those positions are meant to operate those doors, if not for a vacuum leak that I can't track down.

Both door actuators check out good, they open and hold vacuum when I manually apply it, the lines appear to be good but I haven't been able to remove the bulk vacuum plug on the back of the vacuum switching manifold because of a washer on a post that is holding the vacuum line connector in place. I'm worried I will break the post it's on, it's a domed washer with cuts around the inside and it looks impossible to remove without breaking that plastic post. Anyhow, i want to take off that bulk vacuum line connector and disassemble the vacuum switch and see if I could see the problem, I'm told you can take them apart.

Do those vacuum switches go bad? Can you get replacements? Is there a way to get that washer off without breaking the post it's on? Anyone else ever encounter this issue?

 

[yevgenievich]

I have removed the washer carefully before, you can actually clean, regrease(silicone type grease) and add washer during assembly to tighten it. Just did this on my 89 TA as it was leaking

 

[John House]

how did you get it to stop leaking? and how did you remove the washer?

 

[yevgenievich]

how did you get it to stop leaking? and how did you remove the washer?

I pried slowly with a small screw driver. I just added a shim washer when putting back together to tighten the whole assembly(after cleaning and regreasing with silicone base grease). There is a similar method but using bolt and a nut. If the rubber disk inside is too dry, the best solution would be to buy a new assembly. It is still available for later squares, but not sure on the early ones if it is the same.

Here ia example of bolt/nut fix

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[John House]

ah, mine is nothing like that. and it's 34-year old plastic and the washer won't budge, it's very tight and I don't want to break it or it's ruined. I found a guy online who rebuilds them so I'm contacting him.

 

[yevgenievich]

The video skips the locking washer part, but the later squares are similar. Do you have a picture of yours?

ah, mine is nothing like that. and it's 34-year old plastic and the washer won't budge, it's very tight and I don't want to break it or it's ruined. I found a guy online who rebuilds them so I'm contacting him.