TCO Open Error Message

Viper — Troubleshooting — Electronic/Electrical

1. Symptom – TCO Open Error Message

   Each Viper freeze barrel (evaporator) outlet line has a temperature cut off (TCO) sensor clipped to the copper tube.

   Any Viper running R448a refrigerant will have an additional unique TCO clipped to the compressor discharge line.

   All TCO sensors are wired in series with one leg of the 24VAC passing through to power the IO Board and the Motor Control Board.

   If any of the barrel TCO's exceed 120°F (49C), or if the compressor TCO exceeds 275°F (135C), then that sensor will open which then opens the entire TCO circuit, shutting down the refrigeration and barrel motor operation for the entire unit and showing a "TCO Open" error on the display.

   Items to check for:
   1. Verify proper voltage to the TCO circuit (24VAC). A unit Low Voltage error could cause a TCO Open error due to a drop in voltage on the TCO circuit, simulating an open circuit to the control boards.
   2. Hot Gas Solenoid leaking through.
   3. Faulty/loose TCO wiring or harness connections to sensors, boards, or terminal strip.
   4. Unit stuck in defrost cycle.
   5. Faulty TCO sensor for barrel or compressor.