Manitowoc QM 20 User manual

SC - 121-00
Dated: 7/1/00
SERVICE COMMUNICATOR
MANITOWOC ICE, INC. +2110 S. 26th ST., PO box 1720, Manitowoc, WI. 54221-1720 USA
(920-682-0161 •Service Fax [phone] :Web Site - www.manitowocice.com
Subject: QM 20/QM 30 Ice Production, Refrigeration Diagnostics & Charging
The QM 20/QM 30 dice ice cube formation is slightly
different from our previous models. Manitowoc ice
machines have a unique cube shape. It is normal to have a
dimple in the ice cube (a concave indentation in the cube).
Ice cubes from the QM 20/QM 30 may appear to have a
slightly larger dimple than other Manitowoc dice cube
machines. Therefore, cube size for the QM 20/QM 30 is
determined by measuring the slab weight (the combined
weight of all cubes from one harvest cycle). To determine
proper slab weight, follow the instructions listed below.
1. Ensure the air filter, front, and back panels are installed
properly and close the bin door.
2. During the third harvest cycle open the bin door and
catch the entire slab of ice.
3. Weigh the ice slab. The combined weight of all cubes
from one harvest should weigh between 7 - 9 oz
(200 - 270 g). If the slab weight is within this range, the
ice machine is working properly and no further action is
needed. If the slab weight is not within this range or
you desire a slightly thicker or thinner cube, continue to
step four.
4. Remove the air filter.
5. Remove the two screws holding the front panel in place
and remove the front cover.
6. Locate the ice thickness control dial on the control
board (see figure). Turn the dial clockwise for a thicker
cube or counter clockwise for a thinner cube.
7. Assure all of the panels and air filter are reinstalled
properly and the bin door is closed. Repeat steps one
through three.
The QM 20/QM 30 ice machines have a very small
refrigerant charge, 4.59 oz. (130 grams) and we do not
recommend diagnosing the ice machine using refrigerant
pressures. For this reason we have not included refrigeration
access fittings.
Verify that your water flow is even across the entire
evaporator before diagnosing the refrigeration system.
Mineral build-up on the evaporator assembly can cause
water tracking and an erratic ice fill pattern. Clean with
Manitowoc Ice Machine cleaner to remove any mineral
build-up before entering the refrigeration system.
The following can be used for diagnostics:
Capillary Tube failures or low refrigerant charge will always
result in a starving evaporator.
Assume 86°F (30°C) air temperature 68°F (20°C) water
temperature.
Suction line temperature at the compressor will range from
86°F (30°C) three minutes into the cycle to 8°F (-13°C) at
the end of the freeze cycle. An obstructed capillary tube or
low refrigerant charge will have a suction line temperature
higher than normal.
Discharge line temperature at the compressor will range
from 168°F (76°C) to140°F (60°C) through the freeze cycle.
An obstructed capillary tube or low refrigerant charge will
have a lower discharge line temperature than normal.
Suction line temperature at the compressor will range from
64°F (18°C) to 111°F (44°C) through the harvest cycle. An
obstructed capillary tube will not affect suction line
temperature range during the harvest cycle. Low refrigerant
charge will have a lower temperature than normal.
Discharge line temperature at the compressor will range
from 180°F (82°C) to 150°F (60°C) through the harvest
cycle. An obstructed capillary tube will not affect discharge
line temperature range during the harvest cycle. Low
refrigerant charge will have a lower temperature than
normal.
Ice fill pattern will vary depending on severity of the
obstruction or refrigeration loss. Ice fill patterns will range
from no ice on the entire evaporator to thin only at the
evaporator outlet (thin at the bottom, thick at the top of the
evaporator).
After completing the procedure above, if you are unable to
obtain a sheet of ice weighing between 7 - 9 oz (200 - 270 g)
contact the Manitowoc Service Department at
1-800-545-5720 for further assistance.
Ice
Thickness
Control
Dial
WARNING
Disconnect electric power to the ice machine at the
electric switch box before proceeding.

Charging Procedures
QM 20/QM 30 Ice Machines
The QM 20/QM 30 ice machines are critically charged.
There are no refrigerant access ports on these ice machines.
1. Locate the high and low side process tubes.
Install a piercing valve (saddle valve) on both the high
and low side process tubes.
IMPORTANT
Remove piercing valves after charging. Unit is critically
charged.
2. Recovery: Operate the recovery unit as directed by the
manufacturer's instructions.
3. Replace cap tube assembly and line drier.
IMPORTANT
Purge system with nitrogen while brazing to prevent
build up of copper oxide in the refrigeration system.
4. Pressure test system with nitrogen to verify no leaks are
present.
5. Evacuate system to 250 microns. Then allow vacuum
pump to run for an additional 1/2 hour.
REFRIGERANT CHARGE
Important
This unit is critically charged.
Model Refrigerant Type Quantity
QM 20 R 134a 130 g (4.59 oz.)
QM 30 R 134a 165 g (5.78 oz.)
6. Manifold gauges must be removed properly to ensure
that no refrigerant contamination or loss occurs. A
quick disconnect is required for the high side connection
unless high side valve has shut off. Using a digital scale
add the proper refrigerant charge (shown on nameplate)
through the high side.
7. Let the system “settle” for 2 to 3 minutes.
8. Place the toggle switch in the ICE position.
9. Close the high side on the manifold gauge set.
10. Make sure that all of the vapor in the charging hoses is
drawn into the ice machine before disconnecting the
charging hoses.
A. Disconnect the water pump.
B. Run the ice machine in the freeze cycle.
C. Close the high side piercing valve (if required) and
remove the high side hose with the quick
disconnect.
D. Open the high and low side valves on the manifold
gauge set. Any refrigerant in the lines will be pulled
into the low side of the system.
E. Allow the suction pressure to reach 6.89-kPA (0
psi) while the ice machine is in the freeze cycle.
F. Using a pinch-off tool, pinch off the high and low
side process tubes and remove both piercing valves.
G. Using an oxygen/acetylene torch seal the
penetrations from the piercing valves.
Refer to QM 20 Installation Use and Care and Service
Manual P/N 80-1057-3 or the QM 30 Installation Use and
Care and Service Manual
P/N 80-1121-3, for complete service diagnostics.
Contact the Service Department if you require further
assistance diagnosing The QM 20/QM 30 ice machines.
They will need the temperatures as listed on the previous
page, to diagnose the problem.
IMPORTANT
Manifold gauges must be removed properly to ensure
that no refrigerant contamination or loss occurs. A
quick disconnect is required for the high side connection
unless high side valve has shut off.