Thermo King MD-MT, Operator'S Manual

Page: 60 / 192

Electrical Maintenance
60
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. Set the unit for Continuous Run operation and
place the On/Off switch in the Off position.
2. 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.
3. Check the voltage at the B+ terminal on the
alternator. Battery voltage must be present. If
not, check the 2A circuit.
4. Check the voltage at the VOLT SENSE
terminal on the alternator. Battery voltage
must be present. If not, check the 2 circuit.
5. Set the unit for continuous run operation and
place the main On/Off switch in the On
position.
6. Wait 20 seconds for the unloading timer to
de-energize the unloading relay and check the
voltage at the EXC terminal on the alternator.
Battery voltage must be present. If not, check
the EXC circuit.
7. Attach a clamp-on ammeter to the 2A wire
connected to the B+ terminal on the alternator.
8. Connect a voltmeter between the B+ terminal
and a chassis ground.
9. Start the unit and run it in high speed.
10. Connect a jumper wire between the F2
terminal and a chassis ground. This will full
field the alternator.
a. Full alternator output (the alternators rated
output) indicates the alternator is good but
the voltage regulator needs replacement.
b. If there is low or no output, the alternator
is probably faulty. However, the following
items are potential causes for not charging:
• Check the alternator brushes
• Check the 2A circuit from the
alternator to the battery
• Properly tension the alternator belt
• Check battery cable connections and
the alternator ground. They must be
clean and tight
• The battery must be in good condition
and must accept a charge
• Check for excessive or unusual
amperage draw by the unit control
circuits.
Battery
Inspect/clean the battery terminals and check the
electrolyte level during scheduled maintenance
inspections. The minimum specific gravity should
be 1.235. Add distilled water as necessary to
maintain the proper water level.
Charging System
Immediately after start-up, the alternator may not
charge. This is due to light film build-up on the
alternator slip rings. The film build-up occurs
primarily on units that have been sitting unused
for long periods of time. The film should
disappear after a minute or two, and the alternator
should start to charge.
Unit Wiring
Inspect the unit wiring and the wire harnesses
during scheduled maintenance inspections for
loose, chaffed, or broken wires to protect against
unit malfunctions due to open or short circuits.
CAUTION: Never apply battery voltage to
terminal F2 or voltage regulator failure
will occur.