Thermo King KD-II SR, Manual

Page: 71 / 182

Electrical Maintenance (Rev. 04/03)
57
The electric motor has two sets of windings. This test separates the sets.
The start current should begin at 40 to 45 amps, and then drop off to approximately 20 amps in 1 to 3 seconds (in wires T2 and
T2A). After 3 seconds, the run current should stabilize at 4 to 8 amps (in each of the six wires).
Circuit T2A contains the current relay, which controls the motor start contactor. If the start current is in the proper range but
the motor does not shift to run after 3 seconds, go to Test 3. If the start or run currents are very uneven, go to the start or run
capacitor checks in the Troubleshooting Chart.
NOTE: Wire L1A should be connected to the transformer voltage tap that matches the line voltage of the power source.
High voltage on the 208 volt tap will cause high run currents.
Test 3. The unit Starts but does not shift to the run system.
If the motor starts correctly but the current remains at approximately 20 amps after 3 seconds, the start system is not being de-
energized. Use the following procedure.
1. Locate the current relay in the main control panel.
2. Disconnect the 7EA and 7EB wires.
3. Install a switch between the 7EA and 7EB wires.
4. Close the switch between the 7EA and 7EB wires and start the motor.
5. Wait 3 seconds and then open the switch between the 7EA and 7EB wires.
a. If the motor does not shift to run, check for a faulty motor start relay or a faulty motor start contactor.
b. If the motor shifts to run, check for a faulty current relay or an overload on the motor.
c. If the motor shifts to run but then slows down or stops, check for a faulty transformer or faulty run capacitors.
See the Troubleshooting Chart for the individual component tests.