Power Soak 37179 PS-275 Service Manual - Manual (Page 35)

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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 (see section 8.3 for 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. (NOTE: The motor thermo-disc is wired in series with the
heating element thermo-disc, see the schematic for wiring information)
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.