Electrical Maintenance
84
If the voltage at the B+ (POS) terminal is
more than 1.0 Vdc higher than the voltage
between the battery terminals, clean and check
the wires and connections in the 2A and 2
circuits and repeat this check.
17. Increase the charging system load as much as
possible by running run all zones.
18. Monitor the alternator output voltage.
With the increased load, the alternator output
voltage should decrease no more than 0.5 Vdc.
The voltage may increase as much as 1.0 Vdc.
If the alternator output voltage decreases no
more than 0.5 Vdc the alternator is good.
If the alternator output voltage decreases more
than 0.5 Vdc, the alternator is defective if
there are no problems in the wiring. Recheck
the wiring before replacing the alternator.
Alternator Diode Quick Check:
This check confirms proper diode function.
19. With the unit still running, set the digital
multi-meter connected from the alternator B+
output to chassis ground for AC volts
. No
more than 1.0 Vac
should be present. A
reading of more than 1.0 Vac
indicates
damaged alternator diodes.
20. Turn the unit off.
Excessive Voltage Output
12 Volt Alternators With Internal Regular Setting:
When a Thermo King unit is installed on a truck,
it is often connected to a truck battery. When both
the Thermo King unit and the truck engine are
running on the truck battery, the charging system
with the higher voltage may automatically turn off
the charging system with the lower voltage
output.
If it is determined that the Thermo King regulator
setting is higher than the truck charging system or
the batteries are consuming more water than
normal the following solution may help solve the
problem.
• Remove the wire labeled SENSE and tape off.
• Add a jumper wire from 2A to the SENSE
terminal on the back of the alternator.
This should reduce the voltage to the battery by
0.2 to 0.3 of a volt.
Battery
NOTE: The Microprocessor Power switch must
be placed in the Off position before connecting
or disconnecting the battery terminals. The
Microprocessor Power switch is located on the
control box side of the unit.
Inspect/clean the battery terminals and check the
electrolyte level during scheduled maintenance
inspections. A dead or low battery can be the
cause of an ammeter indicating discharge due to
lack of initial excitation of the alternator even
after the unit has been boosted for starting. The
minimum specific gravity should be 1.235. Add
distilled water as necessary to maintain the proper
water level.
Unit Wiring
Inspect the unit wiring and the wire harnesses
during scheduled maintenance inspections for
loose, chafed or broken wires to protect against
unit malfunctions due to open or short circuits.
Electrical Contacts
Inspect all relay contacts for pitting or corrosion
every 1,000 operating hours, and repair or replace
as necessary.
Charging System (12 Vdc)
Immediately after start-up, the voltmeter may
show a low voltage condition on systems with
brush type alternators. This is due to a 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
voltmeter should show a high voltage that will
continue until the battery voltage is brought back
up to normal. If the voltmeter shows low voltage
after start-up, check the alternator belt tension and
all charging circuit connections including the
battery.
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