Thermo King SB-210, Manual

Page: 72 / 159

Electrical Maintenance
72
Fuse Link
The fuse link is located in the positive battery
cable. The fuse link protects the electrical system
from a short in the 2 circuit. If the fuse link burns
out, check for a grounded 2 wire before replacing
the fuse link. Replace this fuse link by replacing
the positive battery cable.
Air Heater
The air heater is mounted on the open end of the
intake manifold. It heats the intake air to help the
engine start in cold weather. The air heater is
energized by the microprocessor during preheat,
just before the engine is started.
The heater is probably defective if the resistance
is more than 0.2 ohms and the current draw is less
than 60 amps, or if the current draw is more than
100 amps.
Check the resistance of the air intake heater with
an ohmmeter between the M6 terminal on the
front of the heater and the screw on the back of
the heater (or the heater case). The resistance
should be 0.1 to 0.2 ohms.
Check the current draw of the heater with a
clamp-on ammeter at the H1 wire near the M6
terminal on the front of the heater. During preheat
the current draw should be approximately 89
amps at 12.5 volts and approximately 77 amps at
11 volts.
Smart Reefer 2
™
Microprocessor Controller
See the SR-2 Microprocessor Control System
Diagnostic Manual TK51587 for complete service
information about the Microprocessor Controller
and the related components.
AC Components
Electrical Contactors
Periodically inspect all contactor points for pitting
or corrosion and repair or replace as necessary.
Test the contactor points by checking the voltage
drop across each set of points when the contactor
is energized and the system is operating. If the
voltage drop across a set of points is more than 15
Vac, replace the contact points as a set.
Test the contactor coil by checking the voltage
across the coil. The contactor coil should be
energized by a minimum of 10 Vdc.
Auto Phase System
The Auto Phase system automatically adjusts the
phase sequence of the power supply to correspond
with the wiring of the electric motor. The main
components of the system are the phase selection
module (PSM), and the two motor contactors
(MC1 and MC2). Contactor MC1 is wired to
retain the phase sequence. Contactor MC2 is
wired to change the phase sequence. The PSM
senses the phase sequence at the heater contactor
and energizes the appropriate motor contactor.
Troubleshooting the Auto Phase System
If the electric motor runs backwards (unit airflow
incorrect):
1. Turn the electric power supply Off and check
the unit wiring. See the appropriate wiring
diagrams, schematics and to Figure 63.
1. M6 Terminal
Figure 62: Air Heater
1
AEA693
CAUTION: Model 50 units use high
voltage ac for electric standby operation.
Lethal voltage potentials can exist on
connections in the high voltage box. Take
appropriate precautions and use extreme
care when testing the unit.