Thermo King UT-1200, Manual

Page: 79 / 169

Electrical Maintenance
79
5. Check and note the battery voltage at the
battery with the unit turned off.
6. With the unit off, check the voltage at the B+
terminal on the alternator. Battery voltage
must be present. If not, check the 2A circuit.
7. Disconnect the main wire harness from the
voltage regulator. On Thermo King
alternators, carefully push on the spring clip to
release the plug lock.
8. Use the Mechanics/Premium HMI Control
Panel to turn the unit on and enter
Non-Running Service Test Mode. Place the
unit in High Speed Cool. Refer to the
appropriate Microprocessor Diagnostic
Manual for information about the Service Test
Mode.
9. Check the voltage at the sense circuit (SENSE
circuit). Battery voltage should be present. If
not, check the sense circuit (SENSE circuit) in
the main wire harness.
10. Check the voltage at the excitation circuit
(EXC circuit). 10 Vdc or more should be
present. If not, check the excitation circuit
(EXC circuit) in the main wire harness.
11. Turn the unit off and reconnect the main wire
harness to the voltage regulator.
12. Attach a clamp-on ammeter around the 2A
wire connected to the B+ terminal on the
alternator. All wires connected to the B+
terminal must pass through the clamp-on
ammeter.
13. Connect a digital multi-meter between the B+
terminal at the alternator and chassis ground.
14. Turn the unit on and allow it to start. Using the
clamp-on ammeter, check the current flow in
the 2A wire.
A positive reading indicates the alternator is
charging. On unit startup, the current flow
should momentarily increase to allow for
battery current used during preheat and
cranking. Within a short time the current
should fall to normal unit load plus charge
current to the unit battery (typically 5-10
amps).
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 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).
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.
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.
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.
CAUTION: Energizing the circuit with
the resistor bypass fuse installed will
damage Thermo King alternators. Be sure
the resistor bypass fuse is removed for
Thermo King alternators.
Temperature 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