Electrical Maintenance
58
High Water Temperature Switch
(HWT)
The HWT will close and trip the reset switch if
the coolant temperature is greater than 220 F
(104 C). Use a continuity tester to check the
switch, and use a coolant temperature gauge to
check the temperature.
1. Remove the 20A wire from the HWT.
2. Run the unit until it reaches normal operating
temperature, approximately 180 F (82 C).
There should be no continuity from the HWT
to ground.
3. If the engine runs hot and the reset switch
does not trip, run the unit until it reaches 220 F
(104 C). The HWT should have continuity to
ground.
Replace the switch as necessary.
Low Oil Pressure Switch (LOP)
The engine oil pressure should rise immediately
after the engine is started. The LOP will trip the
reset switch and stop the engine if the oil pressure
drops below 10 ± 2 psi (69 ± 14 kPa). A
continuity tester is needed to check the LOP.
1. Remove the 20A wire from the LOP.
2. The continuity tester should indicate a
complete circuit between the terminal and
ground.
3. Start the engine. The tester should show an
open circuit between the terminal and ground.
Repair consists of replacing the LOP.
Circuit Breakers
Main Circuit Breaker
This 50 amp auto reset circuit breaker protects
2A, the main power circuit.
If the circuit breaker opens:
1. Check for a short in one of the glow plugs.
2. Check for a ground in the 2A or H circuits.
Control Circuit Breaker
This 30 amp auto reset circuit breaker protects the
unit control circuits.
If the circuit breaker opens, check the unit for a
grounded wire or a grounded condition in a relay
or solenoid.
Evaporator Circuit Breaker
These 40 amp auto reset circuit breakers protect
the fan relays and the evaporator fan circuits. If
the circuit breaker opens, check the evaporator
fans, the fan relays, and the 2D, 2F, FM, and FM1
or the 2C, R2F, RFM, and RFM1 circuits.
Fan Circuit Breakers
These 30 amp auto reset circuit breakers protect
the evaporator fan circuits. If the circuit breaker
opens, check the evaporator fans, and the 2F, FM
and FM1, or the R2F, RFM and RFM1 circuits.
7X-CH Circuit Fuse
This 3 amp fuse is located near the bottom of the
relay board. It protects the 7X-CH circuit, which
grounds the control coil on the 4K relay when the
2K relay is not energized.
If this fuse burns out, check for a short circuit in
the 7X circuit, or check the control coil of the 4K
relay for a short circuit.
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