potential relay failure

[phvac]

Two Potential Relays were installed in this 3 door freezer and both potential relay coils burnt open. The compressor is a semi hermetic Copeland (208/230- 1phase) with start and run caps in the circuit. The cap’s measure good when tested and the compressor windings ohm out R to C = 1.4 ohms, C to S = 4.2 ohms, R to S = 5.3 ohms.

This is an older Universal –Nolin 3 door reach in which ran well for the 1st hour after it was properly charged and dropped the temp 30f. It has no pressure controls just a thermostat which is new. I mention this because before both potential relay coils went open after it short cycled a few times. I don’t know why it short cycled because the thermostat contacts were closed. The Protector disc in the terminal box is also good and does not open until the coil burnt up and the potential relay contacts closed engaging the start windings. I don’t know what caused the potential relay coil to blow.

Any advice would be greatly appreciated.