I just got my 1981 Mercedes 300SD back after changing the a/c system from R-12 to R134a. I ordered all new parts from Performance Products, compressor, switches,dryer located behind headlight driver side, expansion valve located under dash drivers side, and provided PAG150 8oz, plus 2oz of BG fridge quite w/dye. The shop where I take my car did all the work. I was informed that they did not flush the system or replace the expansion valve. They said they did not have the right tools for the valve and that the system was clean. I had replaced all of the above 6 years ago but decided to make the switch. The problem now is that I can only get a 20 degree difference between the outside temp. and the temp. out of the vents. They got 35psi on low and 125-150 on high. Outside temp. was 77 degrees and vent temp. was at 58. Thats only 20 degrees different I excepted 30. Any suggestions would be welcome as I hate to open the system back up but that looks like that need to be done. Thanks NOTE: Just got back from a 100 mile run outside temp. was 83 degrees with vent temp. at 57 degrees. I would also add that the 2oz of BG oil was added in low side after unit was fully charged. UPDATE: I removed 6 ozs. of R-134a and the oil that came out with it and took the car on a 250 mile run, got the vent temp. down to 45 degrees, more that the 30 I was expecting. Advice, you can not use the sight glass to charge a 134a system, it is only there for R-12.