Thermo King SB-210, Manual

Page: 66 / 159

Electrical Maintenance
66
• Make sure the drive belts and pulleys of the
charging system are in good condition and are
adjusted properly before testing the alternator.
Worn belts and pulleys or loose belts will
lower the output of the alternator.
• The battery must be well charged, the battery
cable connections must be clean and tight, and
the 2A and excitation circuits must be
connected properly.
NOTE: All voltage readings should be taken
between the negative battery terminal, or a good
chassis ground, and the terminals indicated,
unless stated otherwise.
1. Check to make sure that the F4 fuse has been
removed from the interface board. If not, it
must be removed, however, the voltage
regulator has probably already been damaged.
2. Press the
O
FF
key to turn the unit off.
3. Check the battery voltage. If the battery
voltage is less than 12 volts, the battery must
be charged or tested to determine if it should
be replaced.
4. Check the voltage at the B+ terminal on the
alternator. Battery voltage must be present. If
not, check the 2A circuit.
5. Disconnect the alternator harness from the
voltage regulator by carefully pushing on the
spring clip to release the plug lock.
6. Press the
O
N
key to turn the unit on. Access
the Service Test Mode screens in the
Maintenance Menu before the unit starts.
Energize the run relay in the interface board
test. See the appropriate Diagnostic Manual
for specific information about the Service Test
Mode.
7. Check the voltage at the A pin and at the B pin
in the two pin connector on the alternator
harness.
a. The A pin is the battery sense circuit and
should be at battery voltage. If not, check
the sense circuit (2 or equivalent) in the
alternator harness and in the main wire
harness.
b. The B pin is the excitation circuit and
should be at 10 volts or higher. If not,
check the excitation circuit (7K or
equivalent) in the alternator harness and in
the main wire harness.
8. If battery voltage is present on the sense and
excitation circuits, connect the alternator
harness to the voltage regulator and check the
voltage on the B pin in the two pin connector
on alternator harness. The voltage should be
0.7 to 1 volt using the interface board test.
a. No voltage or a voltage reading below 0.7
volts indicates that the rotor or the voltage
regulator may be shorted. Perform the
field current test to further isolate the
problem.
b. A voltage reading above 3 volts indicates
that the field circuit may be open or have
high resistance. The brushes or the rotor
are probably defective.
9. Attach a clamp-on ammeter to the 2A wire
connected to the B+ terminal on the alternator.
10. Connect a voltmeter between the B+ terminal
and a chassis ground.
11. Start the unit and run it in high speed.
12. Connect a jumper wire between the F2
terminal and a chassis ground. This will full
field the alternator.
13. Check the amperage in the 2A wire and record
the reading. Check the voltage at the B+
terminal and continue to observe this voltage
for a few seconds to see if it increases,
decreases, or stays the same. Note the change
in voltage and record the voltage reading.
Amperage in the 2A wire =____amps.
Voltage at the B+ terminals =____volts.
The voltage at the B+ terminal should be 13 to
18 volts and the amperage in the 2A wire
should be at least as high as the rated output of
the alternator.
CAUTION: DO NOT full field the
alternator for more than seven seconds
while checking the meter readings, or the
electrical system may be damaged.