TK 56433-5-MM-EN
27
•
A reading on the clamp-on ammeter at or near 0
amps indicates the alternator is not charging.
Checking the unit ammeter will show a
discharge condition. The alternator is defective
if there are no problems in the wiring. Recheck
the wiring before assuming the alternator is
defective.
15. Check the voltage at the B+ terminal. The voltage
should increase until it reaches the anticipated
voltage regulator setting as shown in the table
below. Record the voltage.
•
The voltage regulator setting varies inversely
with the temperature as shown in the table
below. Regulator voltage can vary from
approximately 15.2 Vdc at -40 F (-40 C) to
approximately 13.2 Vdc at 176 F (80 C).
Tempera-
ture
Anticipated Regulator
Voltage
-40 F (-40 C)
From 15.2 Vdc to 14.0 Vdc
77 F (25 C)
From 14.4 Vdc to 13.6 Vdc
176 F (80 C)
From 14.2 Vdc to 13.2 Vdc
•
If the voltage does not increase to the
anticipated voltage regulator setting, the
alternator is defective if there are no problems
in the wiring. Recheck the wiring before
replacing the alternator.
16. If the voltage does increase until it reaches the
anticipated voltage regulator setting, compare the
voltage at the B+ terminal to the voltage between
the battery terminals. The voltage at the B+ terminal
should be no more than 1.0 Vdc higher than the
voltage between the battery terminals.
a.
If the voltage at the B+ terminal is no more than
1.0 Vdc higher than the voltage between the
battery terminals, continue with Step 17.
b.
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 the unit in high speed heat.
18. Monitor the alternator output voltage.
a.
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.
b.
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.
19. A
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e:: This check confirms proper diode function.
a.
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.
Field Current Test
Use this test to determine if the alternator can be
repaired. Perform this test with the unit turned off.
1. Attach a clamp-on ammeter to the 2A wire near the
B+ terminal on the alternator.
2. Energize the field on the Thermo King alternator by
connecting a jumper wire between the F2 terminal
and the B+ terminal. Do not connect the F2 terminal
to ground or the alternator will be damaged.
3. Note the ammeter reading. The ammeter reading
indicates the field current, which should be 2.0 to
6.0 amps at 12 volts.
a. No field current or a low field current indicates
an open circuit or excessive resistance in the
field circuit. Remove the voltage regulator and
brush assembly and inspect the slip rings. If the
slip rings and are acceptable, install a new
voltage regulator and brush assembly and
repeat the test. If the brushes are not the
problem, replace the alternator.
b. High field current indicates a short in the field
circuit. Replace the rotor or the alternator.
Battery
Filler Cap Batteries
1.
Inspect/clean the battery terminals and check the
electrolyte level during scheduled maintenance
inspections.
2.
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.
3.
The minimum specific gravity should be 1.235.
4.
Add distilled water as necessary to maintain the
proper water level.
Maintenance Free Batteries
1.
Inspect/clean the battery terminals and check the
electrolyte level using the integrated sight glass
during scheduled maintenance inspections.
2.
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.
