I've been having trouble with the air conditioning in my 87 CSX and am wondering what the cause could be. The system is original with the exception of R-134a oil and refrigerant. After I run the system for about 10-15 minutes, the compressor will seize and the clutch will begin slipping. I noticed the air isn't terribly cold, and the heat isn't very warm. My guess is that the evaporator isn't evaporating the liquid, causing the compressor to compress a liquid. After I turn off the air conditioning for a while, the compressor will turn again and the system will run without troubles. I have run 134a in 2 other R12 systems without this problem, so I'm hoping that I just have a clogged heater box. Let me know what you guys think.