A used copeland condensing unit,M#C7D8-0750TFC001, was installed for a new walk in freezer. The unit use to be 502 and it's been changed to one shot. The mineral oil was removed and AB oil installed. The txv is new and the head says 502, but I did notice that the bulb is installed after the equalizing line. While I was charging this system up I noticed that the liquid pressure out of the receiver would be 310psi(118F) and the suction pressure before the CPR valve would be 36psi(5F), box temp@32F, compressor superheat 25F, evap superheat 22F, 6F subcooling after receiver, and sightglass full. After running for about 10-15mins the pressures would drop to 270psi(108F) and 25psi(-6F) with bubbles in the sight glass. I would also have 7F evap superheat with 9F compressor superheat before the accumulator and CPR valve. This would happen every 15mins, the changing in pressures. It seems like I have a partial restriction once in a while, I think. The beginning passes are all freezing evenly, but the last passes are still warm. Could the evap be flooded with oil? How can I check? Or should I be relocating the tx bulb to before the external equalizing line. I still need to return to this job Monday, any input is appreciated.