Thermo King 914 724, Manual

Page: 39 / 111

29
Electrical Maintenance
UNIT WIRING
Periodically inspect the unit wiring and the wire harnesses
for loose, chafed or broken wires to protect against unit mal-
functions due to open or short circuits.
REMOTE CONTROL BOX COMPONENTS
NOTE: Use a Fluke 77 or an equivalent meter for all tests.
Testing the Thermometer
Check the Thermometer Display
1. Turn the unit ON (both On-Off switches must be ON).
Note what appears on the thermometer display and
refer to the diagnosis chart to see what to check next.
a. Normal display (-40 to 199 F [-40 to 93 C])
b. Blank Display
c. Erratic Display
d.
e. 1, -00, or -55
Check Power
1. Make sure the master On-Off switch is ON.
2. Open the remote control box cover.
3. Turn the remote control box On-Off switch ON.
4. Check the voltage between the 8X circuit (+ terminal)
and the CH circuit (- terminal) on the back of the ther-
mometer. Battery voltage (12 or 24 volts) should be
present.
5. If battery voltage is not present, check:
a. The wiring, connectors, and components in the
power circuit (8X, 8, 2B, and 2A) to the battery.
b. The wiring, connectors, and ground connections in
the ground circuit (CH) to the battery.
6. If there are no faults in the power circuit or the ground
circuit, check the sensor and the sensor circuits.
7. If there are no faults in the sensor or the sensor circuits,
recheck the thermometer display. If the thermometer
display has not changed, the thermometer is defective
and must be replaced.
Thermometer Display Diagnosis Chart
Temperature
Display
Normal Display No Problem
Blank Display
1. Check Power
2. Check Sensor and Sensor Circuits
3. Check for Reversed Red and Black Wires
Erratic Display
1. Check Power
2. Check Sensor and Sensor Circuits
⊥
Check Sensor and Sensor Circuits
1, -00, or -55 Check Sensor and Sensor Circuits
⊥