Manitowoc Q450 Service Technician's Handbook page 86

2. Extremely Thin at Evaporator Outlet
There is no ice, or a considerable lack of ice formation,
on the top of the evaporator (tubing outlet).
Examples: No ice at all on the top of the evaporator,
but ice forms on the bottom half of the evaporator. Or,
the ice at the top of the evaporator reaches 1/8 in. to
initiate a harvest, but the bottom of the evaporator
already has 1/2 in. to 1 in. of ice formation.
Possible cause: Water loss, low on refrigerant, starving
TXV, hot water supply, faulty water fill valve, etc.
3. Extremely Thin at Evaporator Inlet
There is no ice, or a considerable lack of ice formation
on the bottom of the evaporator (tubing inlet).
Examples: The ice at the top of the evaporator
reaches 1/8 in. to initiate a harvest, but there is no ice
formation at all on the bottom of the evaporator.
Possible cause: Insufficient water flow, flooding TXV,
etc.
4. Spotty Ice Formation
There are small sections on the evaporator where
there is no ice formation. This could be a single corner
or a single spot in the middle of the evaporator. This is
generally caused by loss of heat transfer from the
tubing on the backside of the evaporator.
5. No Ice Formation
The ice machine operates for an extended period, but
there is no ice formation at all on the evaporator.
Possible cause: Water inlet valve, water pump,
starving expansion valve, low refrigerant charge,
compressor, etc.
Q1300, Q1600, and Q1800 model machines have
left and right expansion valves and separate
evaporator
independently from each other. Therefore, one may
operate properly while the other is malfunctioning.
Example: If the left expansion valve is starving, it
may not affect the ice formation pattern on the right
side of the evaporator.
Important
circuits. These
–76–
circuits operate