General Theory of Operation

The controller uses advanced solid-state integrated circuits to monitor and control unit functions. The controller monitors inputs from:

  • Return air sensor

  • Supply air sensor

  • Evaporator coil sensor

  • Ambient sensor

  • USDA (Spare) sensors 1, 2 and 3

  • R-134a compressor discharge line temperature sensor

  • R-23 compressor discharge line temperature sensor

  • Phase measuring circuits

  • Current measuring circuits

  • Voltage measuring circuits

Output signals from the controller automatically regulate all unit functions including:

  • Compressor operation

  • Condenser fan operation

  • Evaporator fan motor operation

  • Liquid line solenoid valve

  • Electric heaters

  • Phase selection

Parent topic: Microprcessor Controller

Frozen Loads (Setpoint at -10 C [14 F] and Below)

Note CRR DF units are designed to haul deep frozen cargo only at setpoints between -10 C (14 F) and -70 C (-94F).

At setpoints of -10 C (14 F) and below, the microprocessor controls unit operation based on the return air sensor temperature and setpoint temperature.

The system operates on Full Cool to provide accurate control of frozen cargo. If the return air sensor becomes disconnected or fails while it is being used to control unit operation, the controller will automatically operate the unit continuously on Full Cool.