Manitowoc QD0202A, Service Manual

Page: 143 / 175

Section 7 Refrigeration System
Part No. 80-1100-3
7-31
LOW ON CHARGE VERIFICATION
The remote ice machine requires more refrigerant
charge at lower ambient temperatures than at higher
temperatures. A low on charge ice machine may
function properly during the day, and then malfunction at
night. Check this possibility.
If you cannot verify that the ice machine is low on
charge:
1. Add refrigerant in 2 lb. increments, but do not
exceed 6 lbs.
2. If the ice machine was low on charge, the
headmaster function and discharge pressure will
return to normal after the charge is added. Do not let
the ice machine continue to run. To assure operation
in all ambient conditions, the refrigerant leak must
be found and repaired, the liquid line drier must be
changed, and the ice machine must be evacuated
and properly recharged.
3. If the ice machine does not start to operate properly
after adding charge, replace the headmaster.
FAN CYCLE CONTROL VS. HEADMASTER
A fan cycle control cannot be used in place of a
headmaster. 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.