I have a client with a walk-in cooler problem or bad pressures, the unit cools but I don't like it. There are 2 evaporators and the cooler size is about 3000 sq ft, anyhow the one evap i replaced in the winter, the other is original, the compressor was replaced 2 years ago as well as the oil sensor and pump. The system was going off on low oil pressure, due to the differential being around 10 psi, the sight glass on the crankcase was clear, you can see the droplets of oil when the system is running, I figured that i needed to add oil because maybe the old coil had a lot of oil left in it that never went back to crankcase so i added a quart, the oil pressure went up to about 60-65 psi with a suction of 40-45, the suction press on r-22 is 40, the hi side is 200, ambient is 70 deg, receiver has 65 pd capacity, i have 53 pds in it with a full sight glass. I can't get the suction press up, the coils are clean, and the txvs are cranked open, the superheat is still too high at 18 deg, subcooling is 6 deg , could need more refrigerant but the sight glass was full 5 pds ago, so i have not added anymore, but the signs point to the system still being low, the box temp is down to 39 deg with these pressures, but i don't like the low suction pressure. Any help is appreciated.