I have a 1996 Cadillac Seville 105K miles. My AC wasn't blowing very cold. After some research I determined that my orifice tube was dirty. When I took it out, it was filthy. I put in a replacement and a new accumulator since the system had been opened up. I pulled a vacuum to take any condensation from the system. After I was done, I left the vacuum motor hooked up for a half hour to make sure I didn't have any leaks. After a half hr, the needles were still pegged in the negative, so no leaks. I put some new refrigerant in the car. I didn't completely fill it, but it was ice cold, so I stopped short of completely full. This was in Sept and it was ice cold. After the weather started to cool down, I didn't use it for a few months. When I turned it back on the other day, it said low refrigerant and the compressor had shut off automatically. What could have happened? Could a high or low pressure switch have gone bad after refilling? It's almost like the refrigerant leaked out, but wouldn't a leak have shown up after I pulled a vacuum on the unit? Thanks!