With engine off the pressures should equalize - IIRC...
It could also be the evaporator behind the drier if the compressor is good..
I just re-read this thread, and if all the facts are correct, you are severely overcharged.
Somebody said that 2lb is a full charge. You had pressure in your system already and you added a 12oz can and 18oz can of freon. That is 30oz. 2lb=32oz. If your a/c was working before, even a little, you probably had at least a pound in the system. Not good.
If you have a partially restricted orifice, your freon pressures will act just like this. If you have a dirty evaporator (air side), your pressures will act just like this.
I would verify what the full charge is. There should be a sticker or something by the compressor that says what the charge should be. Adding more freon is not the answer.:badidea: