What is the story on the high side A/C Schrader valve?
Here is a picture of the low side which looks like an ordinary Schrader valve that's been used for decades.


Here is a picture of the high side, which does not look like an ordinary Schrader valve. It's some type of rubber thingy. I can depress it. But it does not seal after I serviced the system. Some information on the web indicates it might be one-time-use. Is that true? If so, why did GM use this ridiculous method?

 

Not sure, I don’t mess with the AC high or low side anymore.

 

The ball valve has been known to leak. I found this at rockauto.com, might be good for you.

 

My home AC got nearly trashed when a tech hooked his gauges up to the "King" valve to check the pressure then didn't bother to seal the cap. All of the freon leaked out in 2 weeks.
Another tech (grand son) explained that was the most frequent source of a leak in older systems. If the unit is more than 10 years old they always want to replace it after they cause the leak. Mine is now 33 years old, that was the only problem except the welded up contactor (HVAC speak for relay) at 20 years.

 

The following image is what I bought. It has an actual Schrader valve, which obviously means the system is repeatedly serviceable.



My main question is why GM used the ball valve? Various web sources indicate it is one-time-use. Obviously, the A/C system gets serviced in its lifetime, so why would it make sense to put a one-time-use valve on its service port? It would be like putting one-time-use valves on tire stems. Dumb!

 

Maybe, your was "lost during servicing".

It is not a one-time item you just need the adapter. I would bet that certified AC guys have a drawer full of them.

I know mine had plastic covers on them.

 

Well, when you have down time with nothing to do, you can track down the engineer that designed it and/or the person(s) that approved the design, and ask them. We are not part of GM, so asking here is a waste of time.

 

Just speculating, it may have been that the ball valve was deemed to be safer on the high side. I don’t know enough about it to know whether that’s plausible or not. I think we can safely discount the “one use” idea though, even if plausible that the engineers didn’t care about re-use, as it is successfully reused all the time. And I think that valve was intended to be tightly capped when not in use.

 

When I had my ac vacuumed and refilled, the tech changed both high and low pressure schrader valves

 

I wish you the best of luck next time you have to service your system. I'll bet there's a lackluster 50% chance it works for you. Searches around the web indicate this is a problem on many GM vehicles.