Test Procedures - Compressor - Scotsman Prodigy Elite MC0322 Service Manual

MC0322 through MC2148
Air, Water, and Remote Cooled Service Manual
Test Procedures -
Compressor
Failure to start.
Single phase models. All have resistance start, capacitor run type motors. Check voltage to compressor at the
contactor. Compare the idle voltage (compressor off) to the active voltage (compressor starting). The supply
voltage must not be less than the lowest rated voltage for the ice machine. If the voltage is correct, proceed to
the next step.
Check starting components. Most models use a PTCR to cut power to the start winding after the compressor
has started. Check the PTCR for resistance. The resistance check must be when the PTCR is at room
temperature – any temperature between 50 and 100.
At that temperature resistance should be very low between 25 and 50 ohms. Also check resistance to ground,
it should be infinite. If the PTCR is good, check the compressor windings.
Measure resistance from Common to ground. It should be infinite. Measure resistance from Common to Run –
compare to the chart. Measure resistance from Common to Start – compare to the chart.
Compressor check for high amp draw. Measure amp draw of starting circuit. If it does not drop off immediately
after start up, the PTCR should be replaced. It is not practical to check a PTCR for resistance at high
temperatures as the resistance drops very fast as the PTCR's temperature falls. If the compressor is drawing
excessive amps but is operating, the run capacitor may be open. Disconnect electrical power, discharge the
capacitor and measure its resistance. If open, replace it. If shorted to ground, replace it.
Any time the compressor is replaced, the PTCR and run capacitor should also be replaced, or if the model
was equipped with a potential relay, start capacitor and run capacitor, those should be replaced with the
compressor. Most Scotsman service compressors include those parts.
Some systems use a potential start relay and start capacitor in place of the PTCR.
Potential relay. If the compressor will not start, check the amp draw of the starting circuit. If very low, the
potential relay contacts or start capacitor may be open. Measure the resistance of the potential relay contacts
and the start capacitor. If either is open it should be replaced. If the compressor starts but draws very high
amps from the starting circuit, the potential relay may not switch off. In that case the relay should be replaced.
January 2022
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