Ptcr – Scotsman CME1356 User Manual
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PTCR
The “D” series cubers use a PTCR (Positive
Temperature Coefficient Resistor) in place of a
conventional start relay and start capacitor.
Power from the contactor connects to the PTCR and
to the Run Capacitor
A wire connects the other terminal of the PTCR to
the compressor’s start winding.
Another wire connects the run capacitor to the start
winding.
A parallel circuit connects power from the contactor
to the Run winding of the compressor.
A PTCR changes resistance sharply when its
temperature changes. When the PTCR is cold, it
connects full current to the compressor’s start
winding. After a very short time, the PTCR heats up
and shuts off the current flow. Under normal
conditions, the PTCR’s case is at about 180oF.
At that temperature the PTCR has very high
resistance and will not allow current to flow. It must
cool down to about 120oF. Before current will pas
through it again.
Diagnosis:
1. Disconnect electrical power.
2. Check if the PTCR is cool enough to handle
safely. If not, wait 5 minutes for it to cool off.
3. Disconnect both leads to the PTCR and measure
its resistance with an ohmmeter. If the PTCR reads
less than 21 ohms or more than 39 ohms, replace
CME1356 and CME1656
May 2000
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