John House
Junior Member
- Joined
- Aug 3, 2017
- Posts
- 11
- Reaction score
- 4
- Location
- Ohio
- First Name
- John
- Truck Year
- 1974
- Truck Model
- C20 Cheyenne Super Trailering Special
- Engine Size
- 454
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?
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?