I'm putting my truck back together after painting it and decided to look at why I cannot change the heat/air from vent to panel to floor etc... When I manually force each vacuum diaphragm the air switches, but by using the selector it will not switch away from defrost. Is the vacuum selector switch a common fault here? I cannot see or hear any signs of leaks or cracks in any of the lines. They appear to be almost new/very good condition. When I force one of the diaphragms shut then I can hear a faint leak at the switch. Any ideas/ things to check?

 

My '74 is doing the same thing (ever since it came back from the body shop).
I can slowly move it between positions (off-to vent to a/c to blend to defrost to heat) and it will change, but it is like the selector is out of adjustment.
Could it be that some of the body shop dust and stuff is clogging it up in there?
Can I spray WD-40 or something inside without damaging it?

 

What might be the issue there is that the selector is sort of a wheel shape and it rotates on a spindle with springs keeping the tension. If that spindle came undone or unseated from its position I could see it being difficult to rotate. My problem is not that it is difficult to move however. Actually mine moves perfectly. There is a vacuum leak in my situation because none of the vaccum motors will actuate. I can manually work them and then the air blows out in their correct location. But just by using the selector, nothing happens and its stuck in defrost.

 

Mine moves freely, but you almost have to be "in between" positions for the doors to move to the proper positions. Weird.

 

Thats interesting. Maybe that whole selector is bad. Thats kinda why I posted in the beginning to see if these things were a common problem.

 

I have had this happen before. The switch moved freely, and you could not feel it "click" into each position like you can with a good switch. The switch was broken and not routing vacuum to the appropriate channels. In my case, though, you could hear it "hissing" as it leaked.

Also check that you actually have vacuum running to the switch. Vacuum is sourced from a vacuum reservoir under the hood, which itself is sourced from manifold vacuum through a check valve.

 

Yeah, it is a weird deal. I'm kind of afraid that it may be broken as well. Is that piece replaceable or do I have to locate an entire assembly?
YOu can't hear mine hiss except when you change between positions - but I think all of them made a short hiss as you moved between positions.

 

Bump for a resolution?

My 75' is having this issue and trying to sort it out.

THanks

 

I found a used one on Ebay and installed it. It took longer to drop my radio down out of the way then it did to swap the selector switch out. It now works like a charm. Each position changes the airflow and it now supplies power to the A/C compressor.
You will need to look but I think that 73 and 74 are the same. I'm not sure about 75.
Does yours have A/C or just a heater and vent?

 

Wait, the switch is supposed to click into position?? mine works but doesnt click.

 

Mine is moving freely with no resistance between vent ac defrost etc and only blowing out of defrost, coincidently after coming out of body shop as well, guess thats got to be added to the list.

 

It won't "click" but you can feel like a "detent" in each position. Sort of a place when it feels like it has a position and doesn't just slide freely.

 

Mine just slides freely. It changes from defrost to vent. Weird.

 

Hoping it's the cure for mine. Couple little things like this are the only things keeping me from enjoying my truck.

But yea, I have factory AC.

 

Its been awhile but I'm now ordering the selector switch. I've seen recommendations on checking for vacuum on certain items such as the canister and check valve. Anyone with suggestions on how to perform this test. ? I do have access to a vacuum tester but not exactly sure how to use it.