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Electrical Maintenance
78
Base Controller Fuse F4
The base controller has a 300 ohm resistor and a
resistor bypass fuse (F4) in the alternator
excitation circuit. The fuse and resistor are
connected in parallel and are located on the base
controller. Removing the resistor bypass fuse
places the 300 ohm resistor in the excitation
circuit as required for Thermo King alternators
(and Australian Bosch alternators). Installing the
resistor bypass fuse removes the 300 ohm resistor
from the excitation circuit as required for
Prestolite alternators. See the specific unit wiring
diagram for exact details.
NOTE: The F4 fuse must be removed from the
base controller on units equipped with Thermo
King alternators. The voltage regulator on the
Thermo King alternators will be damaged if the
unit is turned On with the F4 fuse in place on
the base controller.
Test Equipment for Checking
Voltage and Current
Always use accurate test equipment such as the
Fluke 23 Digital Multi-Meter and the Fluke
Clamp-On Ammeter accessory when checking
alternator circuit voltage and amperage. See the
table below for Thermo King service parts
numbers. Be sure voltages are measured from the
designated terminal to the alternator chassis
ground. All voltages are DC voltages unless
otherwise noted.
Alternator Load Test
Thermo King no longer recommends a full field
test for determining the alternator current output.
Full fielding an alternator can cause increases in
alternator output voltage that may damage internal
alternator or unit components. This damage may
not be readily apparent.
7
1
3
4
5
2
6
1.
B+ Terminal (Positive Output - 2A Wire)
5.
F2 Terminal (Do Not Ground)
2.
B- Terminal (Negative Ground - CH Wire)
6.
Voltage Regulator and Brush Assembly
3.
S Terminal (Regulator Sense - 2Y Wire)
7.
W Terminal (AC Output - WRPM Wire on Standard Units)
4.
L Terminal (Regulator Excite - EXC Wire)
Figure 151: Thermo King Alternator Terminal and Component Locations
Meter
Service
Part
Number
Fluke 23 Digital Multi-Meter
204-1079
Clamp-On Ammeter for above Meter
204-947