Manitowoc S300 Technician's Handbook page 166

FAN CYCLE CONTROL VS. HEAD PRESSURE
CONTROL VALVE
A fan cycle control cannot be used in place of a head
pressure control valve. The fan cycle control is not
capable of bypassing the condenser coil and keeping
the liquid line temperature and pressure up.
This is very apparent when it rains or the outside
temperature drops. When it rains or the outside
temperature drops, the fan begins to cycle on and off.
At first, everything appears normal. But, as it continues
raining or getting colder, the fan cycle control can only
turn the fan off. All the refrigerant must continue to flow
through the condenser coil, being cooled by the rain or
low outside temperature.
This causes excessive sub-cooling of the refrigerant.
As a result, the liquid line temperature and pressure
are not maintained for proper operation.
166 Part Number 80-1479-3 7/10