Cabin won’t pressurize.  Visitor shopping for a 4P was sitting in cabin with a battery charger on the battery supposedly studying the cheltons but I suspect he was pushing every button and switch he could.  Now pressure valve won’t close.  I can hear the dump switch and gear handle switch both clicking in the valve but it doesn’t move up or down.  Removed the valve and checked for travel.  I can manually close it on the bench but it immediately opens again.  With pressurized air flowing in (vacume cleaner hooked up in reverse) I can depress the valve with my fingers and almost get it to seal but it immediately opens.  Is there another safety switch in the pitot system somewhere?  Any idea where?

I’d appreciate any advice.

Thanks,

Tim, N524JG,  LNC4P, Ser# 411