I had this exact same problem. At the time, I just happened to work with a guy whos brother is an A/C expert. He said it was the expansion valve freezing do to moisture in the valve. I bought a new one and he installed it, a dryer, vacuumed the system and recharged for $100(1995). Problem solved. That lasted about 20yrs until my compressor blew. Since then, I've changed it myself once. It's not hard at all. Just takes some time.