My a/c compressor is bad. I bought a new one and a dryer, and an expansion valve. I also bought a R-134a retrofit kit to charge it with. Question, which is the hi and low side? Also, when I install these parts should I get it evacuated before I charge it? I am under the impression that all the moisture and air need to be removed or internal contamination will occur. Thank you for your help. 82 300 SD.