Thermo King 914 724, Manual

Page: 45 / 111

Electrical Maintenance (Rev. 1/99)
35
Check Power
1. Make sure the master On-Off switch is ON.
2. Disconnect the 14 pin connector (cab control box
extension harness) from the back of the cab control
box.
3. Check the voltage between the 8 circuit (pin 8) and the
CH circuit (pin 13) in the 14 pin connector on the cab
control box extension harness. Battery voltage (12 or
24 volts) should be present.
4. If battery voltage is not present, check:
a. The wiring, connectors and components in the
power circuit (8, 2B, and 2A) to the battery.
b. The wiring, connectors, and ground connections in
the ground circuit (CH) to the battery.
5. If there are no faults in the power circuit or the ground
circuit, repeat the Initial TCM Display Test. If the
results of the test have not changed, the TCM is defec-
tive and must be replaced.
Check Sensor and Sensor Circuits
1. Turn the unit ON (both On-Off switches must be turned
ON).
2. Disconnect the sensor from the evaporator wire harness
(three pin connector).
3. Check the voltage between the positive SN3 circuit (pin
C) and the negative SN1 circuit (pin A) in the three pin
connector on the evaporator harness. The voltage
should be 5.0 ± 0.5 volts.
4. If the voltage is not correct, check the wiring and con-
nectors in the SN1, SN2, and SN3 circuits back to the
cab control box.
If there are no faults in the SN1, SN2, and SN3 circuits,
repeat the Initial TCM Display Test. If the results of the
test have not changed, the TCM is defective and must
be replaced.
5. If the voltage is correct, attach a new sensor and check
the thermometer display.
a. If the thermometer display is now normal, the old
sensor is defective.
b. If the thermometer display is not normal, check the
wiring and connectors in the SN2 circuit.
If there are no faults in the SN2 circuit, repeat the
Initial TCM Display Test. If the results of the test
have not changed, the TCM is defective and must
be replaced.
Faulty TCM
Before replacing the TCM make sure that another problem,
such as a loose wire connection or a bad ground, is not caus-
ing the TCM to malfunction.
Thermometer Calibration Test
1. Place the sensor in an ice-water bath for a few minutes
and allow the sensor temperature to stabilize.
2. Check the thermometer reading. It should be 32 ± 1.8 F
(0 ± 1 C).
3. If the thermometer reading is out of calibration, replace
the sensor and repeat the test.
4. If the thermometer reading is still out of calibration, the
TCM is defective.
Thermostat Switch Sequence Test
This test should be performed during scheduled preventive
maintenance operations. Make sure that the thermometer is
calibrated before performing this test.