Thermo King SB-III 30 SR+, Manual

Page: 36 / 120

Electrical Maintenance (Rev. 04/02)
26
• 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 F15 fuse has been removed
from the relay board. If not, it must be removed, how-
ever, the voltage regulator has probably already been
damaged.
2. Set the unit for continuous run operation and place the
On-Off switch in the OFF position.
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 reg-
ulator by carefully pushing on the spring clip to release
the plug lock.
6. Set the unit for continuous run operation and place the
main On-Off switch in the ON position.
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 cir-
cuit (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 1 to 3 volts.
a. No voltage or a voltage reading below 1 volt indi-
cates 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.
CAUTION: DO NOT full field the alternator
for more than seven seconds while checking the
meter readings, or the electrical system may be
damaged.
13. Check the amperage in the 2A wire and record the read-
ing. 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.