I got a call,a walk in cooler in a convient store not cooling.found out that R short.charged to clear sight glass.the box temp cool down to 34F and cycling ok.
Look at the system carefully,it has one comp but two condensers connected in series. One cond is water cooled,the other one ( is air cooled. One receiver downstream of the condensers. Two evap coils connected in parallel.each coil has a tev but both of the bulb not attach to the suction line but hang to sense the air.low side pressure only stay at 38psi max when the box temp at 40F. The SH was 36F at the comp, 25F at the evaps. It has no high side port to check pressure. The tevs covered with ice,but the coils were not.
Anyway,the box temp is ok now,but this system so strange to me. Anyone has any idea? Thanks.