Power Soak 34774 PS-225 Service Manual - Manual (Page 33)

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7.4 Heating Element Thermo-disc
The Heater Thermo-disc is a devise used to detect a high temperature created by the
heating element. If the temperature at the Thermo-disc reaches 135°F, the disc opens,
turning off power to the UPM. The Thermo-disc is located close to the Heater, inside the
Sensor Pad or on the mounting flange of the heating element. To check the operation
of the thermo-disc, turn off the circuit breaker in the wall mounted enclosure that
supplies electrical power to the control panel. Unplug the spade connectors for the
motor thermo-disc (see section 7.2) and locate the yellow wire with the male spade
connector. Locate the connection to the transformer wires that has a grey wire from the
wiring harness and remove the grey wire from the connection. Use an Ohm meter to
measure the resistance across the male spade connector and the grey wire. If this
measurement shows more than one ohm of resistance it will keep the UPM from
operating correctly. Individually check the male spade connection and grey wire for
continuity to the machine ground. Continuity to the ground would indicate a defective
thermo-disc that will need to be replaced. Reconnect the wires after the evaluation is
completed.
7.5 Thermistor
The Thermistor is a temperature sensor located close to the Heater, inside the Sensor
Pad that is mounted to the outside of the wash tank (see section 8.3 for location). The
UPM measures the resistance through the Thermistor, and associates that resistance to
a temperature. The temperature measurement is used to turn the heating element on
and off for controlling the wash solution temperature. To check the Thermistor, unplug
the white connector from the UPM and using an Ohm meter measure the resistance
across the violet colored wires connected to pin 8 and pin 9 of the cable connector
(refer to section 6.0 for pin layout). The UPM will signal an error if it reads a resistance
greater than 430 k and less than 15 k. Replace the Thermistor if the reading indicates
that it is defective.