If it's a pressure switch I would say that the back side of it is directly in the freon. you might get luck and end up with a diaphram. When you unscrew it slowly, if you here some freon escaping I would say to tighten it back in and go to your service ports for the A/C and let the freon out there, it's a schrader valve ( like a normal tire). If you let the freon out slowly your oil in the system won't be let out and you'll just need to have the A/C re-charged, if you go to fast the oil gets decompressed quickly and vaporizes with the freon and you loose it. Having to re-oil the system will be extra $$$.