1/2x1/2HP Cascade chamber problem

[jmcclellan]

Hey all

We just got back from repair a 0.5x0.5 HP cascade thermal chamber, which had the high stage compressor replaced. This is an R404/SUVA95 system.

Unfortunately, it appears the repair guys' test of functionality seems to be 'does it get to setpoint' not 'does everything work properly'. The chamber does acheive low temps, but slower than it should.

The low stage is now exhibiting a problem it didn't before - the overpressure switch is pulsing intermittently, which causes bypass of the evaporator and hence slow cooling. Can anyone give me any ideas of the most likely cause? I can think of a few possibilities, all of which involve poor workmanship. crap in the high system (partial blockage somewhere), improper charge of either system, etc.

Thanks in advance for any ideas!

can anyone confirm, to replace the high stage compressor, would (should?) they have discharged/recharged the low stage system also? their work order identifies only R404 suggesting they did not discharge the low system.. if this is the case, the charging should be the same as before, and since it worked fine before, that would mean that this pressure limit switch problem is probably related to the high stage providing insufficient cooling for some reason or another..