Hussmann Proto-Aire, Installation Manual

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Protocol™ Installation and
Service Manual
Defrost Schedule
Refrigeration Circuit Control
The following circuits show the electrical connections during the refrigeration cycle.
Power comes into the control board from X1A. The refrigeration solenoid valve and
thermostat (if needed) are wired to the terminal pin. The unit cooler circuit is the same as a
simple refrigeration circuit but it has an additional fan control circuit. The fan control
circuit ensures that the fans will not turn on during the defrost cycle. It should be noted
that off time defrost is achieved by turning the refrigeration valve off. For unit cooler fan
wiring see page 87.
Defrost Circuit Control
Off time Sequence of Operation
Control Board energizes the Defrost Board Relay Coil, which open the Main Liquid Line
Solenoid circuit.
Main Liquid Line Valve closes. As evaporators empty, the compressors cycle off on Low
Pressure.
Defrost my be time or temperature terminated.
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