Operating Theory

Magnum+ and CFF Operating Mode Function Chart

Chill Loads Setpoints at -9.9 C (14.4 F) and Above Frozen Loads Setpoints at -10 C (14 F) and Below  
Cool w/Mod Heat Defrost Cool Null Defrost Unit Function
•1 •         Evaporator Fans High Speed1
•1     • •1   Evaporator Fans Low Speed1
    •   •1 • Evaporator Fans Off1
• •         Proportional-integral Derivative (Supply Air) Control
      • •   Return Air Sensor Control
    •     • Evaporator Coil Sensor Control
•     •     Compressor On
•     •     Compressor Vapor Injection On (valve energized)2
•     •     Condenser Fan On3
•     •4     Digital Control Valve Modulating (energized)4
•5 • •     • Electric Heaters Pulsing or On (energized)5

SF Operating Mode Function Chart

Super Freezer Setpoints at -10 C (14 F) and Below  
Cool Null Defrost Unit Function
      Evaporator Fans High Speed1
• •   Evaporator Fans Low Speed1
    • Evaporator Fans Off1
      Proportional-integral Derivative (Supply Air) Control
• •   Return Air Sensor Control
    • Evaporator Coil Sensor Control
•     Compressors On (Compressor High T and Compressor LowT)
      Compressor Vapor Injection On (valve energized)2
•     Condenser Fan On3
      Digital Control Valve Modulating (energized)4
•     Liquid Injection Valve (energized)
    • Electric Heaters Pulsing or On (energized)5

1Setpoint temperature and controlling mode setting determine the evaporator fan speed:

  • Normal Operation: Chill Loads - High or low speed fans; Frozen Loads - Low speed fans or no fans.

2Vapor injection valve:

  • Chill, Frozen, or Power Limit Mode: When the cool capacity is 100 percent.

  • Compressor High Temperature Protection: When the compressor discharge temperature exceeds 138 C (280 F).

3Condenser fan pulses on and off on a 30 second duty cycle to maintain a minimum condenser temperature:

  • Chill Loads: Controller maintains a minimum 30 C (86 F) condenser temperature.

  • Frozen Loads: Controller maintains a minimum 20 C (68 F) condenser temperature.

4Digital Control valve modulates:

  • Chill Loads - whenever the unit is in a Cooling mode; Power Limit - whenever the unit is in Power Limit mode.

  • Dehumidification: When the Dehumidify mode is set to On, the supply air temperature must be In-range to energize the electric heaters.

    • When the humidity is two percent or more above humidity setpoint, the controller (energizes) the heaters.

5Controller energizes electric heaters for heat, defrost and dehumidification:

  • Heat mode (compressor off): If supply air temperature is too low, heaters pulse on and off on a 60 second duty cycle.

  • Defrost mode: Heaters are on until evaporator coil temperature increases to terminate defrost.