Thermo King 914 724, Manual

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Electrical Maintenance (Rev. 1/99)
31
2. Check the power to the thermostat (see Check Power).
3. Turn the On-Off switch OFF and disconnect the sensor
wires from the thermostat (wires SN4, SN5, and SN6
from thermostat terminals T11, T10, and T9, respec-
tively).
4. Check the voltage between the positive SN6 circuit
(terminal T9) and the negative SN4 circuit (terminal
T11) on the thermostat. The voltage should be 5.0 ±
0.5 volts.
If the voltage is not in this range, the thermostat is
defective.
Check the Thermostat Sensor
1. Turn the unit ON (both On-Off switches must be turned
ON).
2. Check the thermometer display. Make sure that the
thermometer is operating properly and note the reading.
3. Disconnect the thermometer sensor and the thermostat
sensor from the evaporator harness (three pin connector
in the evaporator). Connect the thermostat sensor to the
thermometer section of the evaporator harness (wires
SN1, SN2, and SN3).
4. Check the thermometer display now that the thermostat
sensor is attached to the thermometer section of the
evaporator harness. The thermometer should display a
reading approximately equal to the reading observed in
step 2. If not, the thermostat sensor is defective.
Check the Thermostat Sensor Harness and Sensor
Assembly
1. Turn the unit ON (both On-Off switches must be turned
ON).
2. Check the thermometer display. Make sure that the
thermometer is operating properly and note the reading.
3. Disconnect the thermometer sensor harness from the
thermometer sensor wires (3 pin connector).
4. Disconnect the thermostat sensor harness from the ther-
mostat (wires SN4, SN5, and SN6 from terminals T11,
T10, and T9, respectively).
5. Connect the thermostat sensor harness wires to the ther-
mometer sensor wires. Connect wire SN4 to SN1 (red),
connect SN5 to SN2 (white), and connect SN6 to SN3
(black).
6. Check the thermometer display now that the thermostat
sensor harness is attached to the thermometer wires.
The thermometer should display a reading approxi-
mately equal to the reading observed in step 2. If not,
the thermostat sensor harness or the thermostat sensor
is defective.
Check the Potentiometer Circuit
1. Turn the unit ON (both On-Off switches must be turned
ON).
2. Check the power to the thermostat (see Check Power).
3. Check the voltage between the positive T1 circuit
(black wire - T1 terminal) and the negative T3 circuit
(red wire - T3 terminal) on the thermostat. The voltage
should be 0.80 ± 0.10 volts. If the voltage is not in this
range, the thermostat is defective.
4. Check the voltage between the positive T1 circuit
(black wire - T1 terminal) and the setpoint input T2 cir-
cuit (white wire - T2 terminal) while turning the ther-
mostat dial (potentiometer) back and forth. The voltage
should increase to 0.80 volts and decrease to 0 volts as
the dial is turned back and forth. If not, the potentiome-
ter is defective.
5. Check the voltage between the negative T3 circuit (red
wire - T3 terminal) and the setpoint input T2 circuit
(white wire - T2 terminal) while turning the thermostat
dial (potentiometer) back and forth. The voltage should
increase to 0.80 volts and decrease to 0 volts as the dial
is turned back and forth. If not, the potentiometer is
defective.