HVAC selector switch, 1970 Buick GS

[JonW]

My 1970 Buick GS has factory air. The selector switch (selects a/c, heat, defrost, etc) is inop. I bought a replacement switch and it also was inop. I guess the vacuum membrane in them deteriorates over time. I don't drive the car in the winter, so I don't need heat or defrost. Is there a way to lock the system in a/c mode so that air comes out the dash vents?

[rocketraider]

The only way I can think to do that would be to get everything set as you want it and then disconnect and plug the  vacuum source.

 

But then some of those doors have assist springs and would probably default to whatever position they move to on loss of vacuum. To defeat that you'd have to go in the HVAC plenum and physically block the doors in place.

 

Have you tried applying vacuum to the individual vacuum motors to make sure they operate? They are 50+ years old. Maybe older, depending on if earlier carlines used the same part number and they were sitting on the shelf a few years before assembly.

[joe_padavano]

Have you verified that you actually have vacuum at the selector? You might want to try troubleshooting before buying more parts or jury-rigging the system.

[Ben Bruce aka First Born]

One of the times older is better than the interim,   then on to the best. I detest the vacuum controls. My 1992 Roadmaster is vacuum. The "switch" is barely larger than a quarter and fragile.

 

  Ben

[Frank DuVal]

First diagnose if there is vacuum to the switch and the switch is truly inop. 

 

Find a vacuum diagram for the HVAC system and connect the vacuum from the switch to the vacuum/motor holding the plenum door to make air flow from the dash vents. Do you want recirculated or fresh air all the time? I forgot which is the default mode. 

 

The vacuum switch might be repairable. Hey, if it is already broken, maybe someone wants to "take a crack at it".