Unit Protection Devices

High Pressure Cutout Switch (HPCO): This normally closed switch monitors the discharge pressure at the compressor. It opens on high discharge pressure to shut the unit down to prevent damage.

Electronic Throttling Valve (ETV): This component is an electromechanical control device used to limit the suction pressure to the compressor. The valve is controlled by the microprocessor controller.

Preheat Buzzer: The preheat buzzer sounds when the CYCLE-SENTRY system energizes the glow plugs. This should warn anyone near the unit that the CYCLE-SENTRY system is about to start the diesel engine.

Coolant Temperature Sensor: This sensor provides an engine coolant temperature input to the microprocessor. If the engine coolant temperature is too high, the controller stops the unit and records an alarm.

Electric Motor Overload Relay (Model 50): The overload relay protects the electric standby motor. The overload relay opens the circuit from the contactor to the electric motor if the motor overloads for any reason and an alarm will occur. The relay resets when the alarm code is cleared.

Fuses: Sizes and functions are described in the Specifications chapter of this manual.