Ptcr Diagnosis - Scotsman CME1056 User Manual

CME1056

PTCR Diagnosis

The CME1056 "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 180
At that temperature the PTCR has very high
resistance and will not allow current to flow. It must
cool down to about 120
through it again.
o
F. Before current will pas
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 22 ohms or more than 40
ohms, replace it.
o
F.
May 2000
Page 32