Yeah, presure should equalize after a few minutes. Should not take that long. Crazy idea: can you gently whack the expansion valve with a hammer or similar tool? Not sure where it is on your car. Curious if it is stuck and could be "unstuck". I agree with the idea of an overcharge, but I don't think that is the only problem. If there are no R134a service fittings, then you probably have R12. Try not to let that stuff get away. Not to scare ya, but this could get expensive. On the plus side, at least your system does hold a charge