Hoffman Controls 880-90 EC Head Pressure Control

The Hoffman Controls 880-90 Low Ambient Head Pressure Control is designed to modulate energy efficient Electrically Commutated condenser fan Motors (ECM) in air conditioning and refrigeration systems. The 880-90 control varies the speed of the condenser fan ECM motor(s) to vary the air volume through the condenser consequently regulating head pressure for proper heat rejection in low ambient temperatures. The 880-90 Head Pressure Control monitors the head pressure by sensing the sub-cooled liquid line temperature by placing a 10K sensor on the refrigerant liquid line. As the liquid line temperature drops, the motor speed will be reduced to prevent freezing of the coil. As minimum motor speed is reached, the control will cycle the motor off until the liquid line coil temperature has returned to safe operating levels. At this point, the motor will modulate back to full speed to maintain proper heat rejection. The 880-90 control provides an adjustable LOW SET point of 40°F to 80°F and an adjustable HIGH SET point of 60°F to 140°F for the ability to custom tune the control for any application. The common settings for most applications is a LOW SET point of 50°F and a HIGH SET point of 80°F. In this example, the condenser fan(s) modulation from full speed occurs at 80°F liquid line (ambients above 60ºF), and reaches minimum speed at 50°F liquid line (ambients below 30°F). The ECM condenser fan motor cycles “OFF” at liquid line temperatures below 50°F, and cycles back “ON” to minimum speed at 53°F liquid line temperature. The ECM condenser fan motor will modulate from minimum speed to full speed between 53°F and 80°F.