Scotsman NM952R Service Manual page 27

SERVICE DIAGNOSIS: Condition - No Ice Being Produced
STATUS: GEARMOTOR OPERATES, COMPRESSOR DOES NOT
A. Check the pump down control switch.
1. This pressure switch opens at 6-10 psig, and closes at 16-20 psig. If open check the low side pressure,
if after running the machine the switch opens at a pressure higher than 10 psig, replace the switch.
The low pressure control switch could remain open for any of the following reasons: Low refrigerant
charge, auger not turning, restricted system, TXV not opening, liquid line valve not opening.
2. Check the low side pressure, the low pressure cut out switch should remain closed at any pressure
higher than 10 psig. If less than that:
a. Check if the auger is turning, if it is not, remove the gearbox and:
Check for internal damage, repair and replace in the machine.
b. Check for low charge, add some refrigerant, if the unit begins to operate, (normal low
side pressure being about 25 psig) stop and look for a leak, recover, repair, replace the drier,
evacuate, and weigh in the nameplate charge. If, with added charge,
the unit does not operate:
Check for a restricted system, replace the drier, evacuate, and weigh in a
nameplate charge.
Check for a Thermostatic Expansion Valve that does not open, if defective,
replace it. Recover, replace the drier, evacuate, and weigh in the nameplate charge.
c. Check the liquid line solenoid valve, it should have power to it, if not:
Check the connections on the circuit board. The liquid line (or compressor) relay
on the circuit board may have failed. If so, replace the circuit board.
If there is power to the valve, the coil may be open, or the valve jammed, replace
the valve.
November 1992
Page 27
NM952R