Proheat X45–School Bus - Manual (Page 74)

5-17 SECTION 5. TROUBLESHOOTING & REPAIR
An OVERHEAT diagnostic code is displayed when the overheat breaker has
tripped, shutting the heater down. This occurs if the heater has been started
with little or no coolant in the heat exchanger.
Check: Coolant Flow
a) Is there coolant in the system?
b) Determine if there is a blockage or air in the plumbing.
The compressor motor is wired in series with the overheat breaker. The breaker
contains a normally closed thermo switch. When the thermostat reaches the
preset temperature of 286°F (141°C), the contacts OPEN shutting the
compressor and fuel pump OFF, instantly shutting the heater down. It cannot
be restarted until the breaker is manually reset.
To reset the breaker, remove the rubber cap covering the top of the overheat
breaker and press the red reset button on top. If the breaker will not reset, allow
the heater to cool.
Test Procedure:
a) Connect a multimeter (adjusted to measure resistance) to the
overheat breaker connector. (Figure 5-16.)
The sensor should be normally closed. If the sensor has
tripped the circuit should be open.
Figure 5-16 Overheat Sensor Test
RED RESET BUTTON
PLUNGER
SPRING
POLARITY
NOT IMPORTANT
4 Overheat
CAUTION
Do not reset the Overheat breaker
until the cause of the overheat
condition has been determined.