Service manual

Refrigeration System Section 7
7-4
Part No. 80-1206-3
Refrigeration System Diagnostics
GENERAL
Verify the water and electrical systems are functioning
properly before diagnosing the refrigeration system or
it’s components.
A dirty evaporator increases the length of the harvest
cycle and will cause the ice machine to shut off on safety
limit #2. All Manitowoc ice machines must have their
evaporator(s) cleaned first, if safety limit #2 is in
memory.
REFRIGERATION SYSTEM OPERATION
Freeze Cycle
The compressor sends high pressure, high temperature
gas to the condenser.
Air-Cooled Models
- Discharge pressure will exceed the
fan cycle control cut in set point and the condenser fan
motor(s) energizes. The condenser removes heat and
the refrigerant condenser to a high pressure liquid. The
head pressure control valve will modulate to maintain
the correct head pressure and refrigerant temperature.
Water-Cooled Models
- The head pressure control valve
modulates from the bypass position to the non-bypass
position as the head pressure exceeds its set point. The
condenser removes heat and the refrigerant condenses
to a high pressure liquid. The water regulating valve will
modulate to maintain the correct head pressure and
refrigerant temperature.
The refrigerant enter the ice machine head section and
is store in the receiver. Liquid refrigerant leaves the
receiver through a dip tube and passes through the line
drier and liquid line solenoid valve. The refrigerant then
passes through the heat exchanger where the liquid is
sub-cooled before delivery to the TXV. The liquid
refrigerant passes through the expansion valve orifice
and enters the evaporator as a low pressure saturated
vapor. As the refrigerant leaves the evaporator and
passes through the heat exchanger absorbing additional
heat from the liquid line. The suction vapor returns to the
condensing unit, passes through the suction
accumulator and enters the compressor.
Harvest Cycle
The head pressure control valve bypasses the
condenser and sends compressor discharge gas directly
to the receiver. The discharge gas keeps the receiver
warm and the refrigerant pressure up as liquid
refrigerant is boiled off the receiver. Vapor from the top
of the receiver flows through the cool vapor valve and
condenses in the evaporator. The change of state of the
refrigerant from vapor to liquid releases the heat
necessary for the harvest cycle. The refrigerant returns
to the condensing unit and enters the suction
accumulator. Vapor refrigerant is returned to the
compressor.