Trouble Shooting Cascade system W/Cap tube SO LOW U85-18

[aerobat72L]

Hi, Interesting problem. The So-Low is a two-stage Cascade system w/Cap tubes. The system Has two 1HP compressors. The problem I'm experiencing is as follows. Unit Thermostat is set to Minus-40 Deg C. Unit starts normally, and runs down to setpoint. After shutting down at setpoint there is, of course, a deadband idle time. After idle period, unit tries to resume setpoint . Immediately upon restart, unit blows 20-Amp wall breaker. I cannot understand why start from scratch operates properly, but resumption of operation causes this symptom. I guess my question is: What can cause this, and how can I isolate problem. Thanks to anyone with experience in this matter.

[Brian_UK]

Is the low side compressor trying to start without the high side already running?

You say 'idle period', is this a set time period or "just an expression"?

[install monkey]

how long is the delay before restarting-should be at least 3 mins

[Tesla]

Hi Aero
Capp systems use low start torque compressors and require time for the pressures to equalise. You could use a fluke current meter with logging of max current to confirm, could also be starting gear on comp giving you trouuble.

[thebigcheese]

is it set for -40 in the cabnet or is the heat exchanger set for -40 therefore bringing on second stage compressor to cool the cabnet?