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Electrical Maintenance
AC Generator
The AC generator provides electric power during
diesel engine operation. The AC generator is
mounted under the diesel engine and driven by a
belt. The AC generator provides AC power for the
condenser and evaporator fan motors. An optional
battery charger converts AC power from the AC
generator (or the electric standby power source) to
12 Vdc to charge the battery and provide power
for the 12 Vdc control system. The engine speed
determines the output frequency of the AC
generator, which affects the fan speeds.
Test the AC generator output under a load as
follows:
1. Use the Service Test Mode to run the unit in
high speed cool. Refer to the appropriate
Diagnostic Manual for specific information
about the Service Test Mode.
2. Remove the cover from wire connection box
on the AC generator.
3. Check the AC output voltage between the
following terminals: T1 to T2, T2 to T3, and
T1 to T3. Approximately 345 Vac should be
present between each pair. If not, the AC
generator is faulty.
Alternator Diagnostic
Procedures
General Information
Poor charging performance may not be caused by
a bad alternator. The following conditions can
cause improper battery charging, even with a
good alternator. (See Service Bulletin T&T 388
for more information.)
•
A problem may exist in the 2A output circuit
from the alternator to the base controller or in
the 2 circuit from the base controller to the
battery. Check for an open 2 or 2A circuits,
fuse FS8, loose connections, defective battery
cables or dirty battery terminals.
•
The battery must be in good condition and
capable of accepting a charge. Check for a
damaged battery, correct electrolyte level, and
loose or corroded connections.
•
The alternator charging output will be low if
the alternator belt or pulleys are defective or
the belt is not properly adjusted. Be sure the
belt is not loose or cracked and the pulleys are
the correct size and in good condition.
•
The excitation circuit (EXC circuit) must
supply voltage to the excite terminal of the
alternator.
•
The sense circuit (2Y circuit) must supply
voltage to the sense terminal of the alternator.
•
The alternator must be properly grounded.
•
The unit control circuits or installed
accessories may be drawing excessive current.
•
An overcharged battery is usually caused by a
defective voltage regulator.
Alternator Identification
•
These units use Thermo King Alternators (see
Figure 151), which are painted black.
CAUTION: These units use high voltage
AC from the AC generator for the
condenser and evaporator fans. Lethal
voltage potentials can exist on
connections in the fan control box. Take
appropriate precautions and use extreme
care when testing the unit.
