Manitowoc Indigo Series Technician's Handbook page 264

Freeze Cycle Operation All Models
The R404A head pressure control valve is non
adjustable.
At ambient temperatures of approximately 70°F (21°C)
or above, refrigerant flows through the valve from the
condenser to the receiver inlet. At temperatures below
this (or at higher temperatures if it is raining), the head
pressure control dome's nitrogen charge closes the
condenser port and opens the bypass port from the
compressor discharge line.
In this modulating mode, the valve maintains minimum
head pressure by building up liquid in the condenser
and bypassing discharge gas directly to the receiver.
Harvest Cycle Operation
Remote Condenser Models
The head pressure control cycles into full bypass due
to the pressure drop when the harvest valve opens.
Refrigerant flows from the compressor to the
evaporator through the harvest valve and the head
pressure valve is out of the circuit.
264 Part Number Preliminary 6/11