Ok thats probably the sanden unit , have him look at the pressures at idle if they fluctuate take it off and get a good one. I tried for seasons compressors along time ago and they dont last. You can get a new unit for pretty cheap ( bmw conversion uses this compressor on older cars ) Make sure he locates the leak, and fixes it . Then make sure you get your pressures right at idle ( DO NOT go by bubbles in sight glass on 134. you have to put in 15% less 134 than the car originally had r-12. I go by pressure and put a thermometer in the dash and adjust that way sometimes. Good luck.
