Head Pressure Control for Air Conditioning and Refrigeration

  • Description:

The MJB HPC326 operates as a temperature-sensitive, motor fan speedHead Pressure Control for Air Conditioning and Refrigeration Head Pressure Control for Air Conditioning and Refrigeration control. Head pressure is regulated during low ambient temperature conditions by varying the amount of airflow through the condenser coil. This helps ensure sufficient pressure across the expansion valve, preventing costly downtime.

  • Operation:

Upon initial application of power to the controller, the output voltage will be in the “Hard start” mode for a specified period of time. This time may be either factory fixed or field adjustable from 0.1 - 5 seconds. Upon completion of the Hard Start period, the output voltage control reverts to the temperature probe.


Speed control will not occur until the line temperature falls below 40 deg C. Above 40 deg C full voltage will be applied to the motor such that there is no loss in condensing efficiency. As the temperature being sensed decreases, the output voltage to the fan motor will decrease to the determined “Low Temperature Cut-off”.


Upon reaching the Low temperature Cut-off setting, the output voltage will go to zero volts thus effectively turning the fan off until the condenser coil temperature rises above the Low Temperature Cut-off temperature. The Low Temperature Cut-off setting maybe either factory fixed or field adjustable.


The system will restart the fan once the temperature exceeds the “Low Temperature Cut-off” temperature by a pre-determined amount, which is the system hysteresis (Deadband). The hysteresis is factory fixed. Removal of the line voltage will de-energise the output immediately. Re-application of the line voltage will energise the output at maximum voltage for the Hard Start duration, regardless of the value of the thermistor input.

  • Replaces:


  • Data Sheet:

HPC326 Information Sheet
HPC326 Schematic Drawing