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My ventilation knob (right side) isn't working. The knob doesn't feel to be just spinning freely, so it feels like the little u-joint is still intact. I suspect the problem is at the bellcrank on the firewall side of the box, and that it'll need to come out to access it. Has anyone addressed anything like this? I'm hoping this is a simple repair notwithstanding pulling the heater box, as opposed to a cracked gear or some other unobtainium NLA part quagmire.

Eric, Hope you're well. As you may have seen when I replaced my water heater valve, I was in that general area but wasn't ( I don't think ) doing anything to the parts you are describing so I cant really give you much help. I will say though just removing the two console side panels and the radio etc front panel give you way better access to see what your doing. Yes its a PIA but just take your time. Like a lot of these things it seems very complicated but when you actually get in there a see whats going on it will probably be one small broken or loose part. You'll never know until you take a look. Hope it goes well for you.

I agree with maybeillbuyit ....pull the right side panel, maybe a half dozen small screws and have a look with a flashlight . You may be able to see where it's binding.

For the first time, and likely the last, I completely ignored the problem and it disappeared. I don't advise this approach for, say, a persistently cherry-red oil pressure light or a spurting fuel line in the engine bay. I'm sure the ventilation issue will resurface when I next need the defroster.

I finally attacked the evaporator. Boy that thing sure is buried. I found all kinds of electrical "artifacts" from the previous owner during the excavation, which were corrected. It's much easier to do when everything is apart.

The expansion valve was stamped "Made in West Germany" and bore the date 4/81 - when my car was built. I think it was due for replacement.

What's not great about the R12 flare fittings is that I'll need to reconnect the evaporator to the circuit in order to pressure-test the expansion valve fittings. Does anybody have a suggestion for testing while the evaporator is out of the car? There are no known shops in my area that will work on an R12-based system.

I was thinking about replacing the flare fittings on the hard lines at the evaporator to the o-ring fittings, but the length of the hard lines is pretty much right on the money, so adaptors wouldn't work -- I'd need to replace the hard lines. Mission creep!

The likely cause of this problem is the control shaft, which has a connection using two circular discs, one with attached nuts and one with arcuate slots. When the machine screws are loose, the discs can slip. The control shafts are located behind the controls and the universal joints connected to the control knobs.

Use a 90-degree phillips head to tighten the machine screws after ensuring that the shafts are properly aligned. The screw heads face the firewall.