Service manual

Section 7 Refrigeration System
Part No. 80-1206-3 7-19
COOL VAPOR VALVE
General
The cool vapor valve is an electrically operated valve
that opens when energized, and closes when de-
energized.
Normal Operation
The valve is de-energized (closed) during the freeze
cycle and energized (open) during the harvest cycle.
The valve is positioned between the receiver and the
evaporator and performs two functions:
1. Prevents refrigerant from entering the evaporator
during the freeze cycle.
The cool vapor valve is de-energized (closed)
preventing refrigerant flow from the receiver into the
evaporator.
2. Allows refrigerant vapor to enter the evaporator in
the harvest cycle.
During the harvest cycle, the cool vapor valve is
energized (open) allowing refrigerant gas from the
top of the receiver to flow into the evaporator. The
refrigerant changes state (from a vapor to a liquid)
and gives up latent heat. This heat is absorbed by
the evaporator and allows release of the ice slab. In
general, harvest cycle suction pressure rises, then
stabilizes in the range of 65-125 psig (448-861 kPA).
Exact pressures vary according to ambient temperature
and ice machine model. Harvest pressures can be found
in the “Cycle Time/24 Hour Ice Production/Refrigerant
Pressure Charts”.
Analysis
The valve can fail in two positions:
• Valve will not open in the harvest cycle.
• Valve remains open during the freeze cycle.
VALVE WILL NOT OPEN IN THE HARVEST CYCLE
Although the circuit board has initiated a harvest cycle,
suction and discharge pressures remain unchanged
from the freeze cycle. The ice machine will remain in the
harvest cycle for 3.5 minutes, (7 minutes QDUALC) then
initiate a new freeze cycle. After three consecutive
harvest cycles of 3.5 minutes. (7 minutes QDUALC) the
ice machine will stop on a safety limit #2.
VALVE REMAINS OPEN IN THE FREEZE CYCLE:
Symptoms of a cool vapor valve remaining partially open
during the freeze cycle can be similar to symptoms of an
expansion valve or compressor problem. Symptoms are
dependent on the amount of leakage in the freeze cycle.
A small amount of leakage will cause increased freeze
times and an ice fill pattern that is normal.
As the amount of leakage increases the length of the
freeze cycle increases and the amount of ice on the
bottom of the evaporator decreases.
A small amount of leakage will cause an audible
indication as the vapor passes through the valve. As the
size of the leak increases the audible indication
becomes more apparent.
Refer to the Parts Manual for proper valve application.
When replacement is necessary, use only “original”
Manitowoc replacement parts.