Test Procedures - Loads - Scotsman C0530SR-1 Technical Manual

Test Procedures - Loads

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.
September 2006 Page 61