TK 61555-2-MM-EN
31
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.
To test the alternator under load, Thermo King recommends the use of a clamp-on ammeter to
monitor output current, both on initial startup and under full unit load conditions. For example,
on multi-temp units, all remote evaporators should be turned on.
General Diagnostic and Warranty Evaluation Procedure
Complete the following diagnostic procedures before replacing an alternator or the voltage
regulator:
1.
When testing an alternator, use accurate equipment such as a Thermo King P/N 204-1079
digital multimeter and a Thermo King P/N 204-947 amp clamp or equivalent.
2.
Verify the drive belts and pulleys of the charging system are in good condition and are
adjusted properly before testing the alternator. Verify the pulleys are the correct size. Worn
belts, loose belts, and worn or improperly sized pulleys will lower the output of the alternator.
3.
The battery must be charged and in good condition, the battery cable connections must be
clean and tight, and the 2A, 2 (sense), and EXC (excitation) circuits must be connected
properly. All charging circuit connections must be clean and secure.
N
No
otte
e:: If the unit battery is questionable, a known good jumper battery should be substituted
for alternator testing.
N
No
otte
e:: Do not perform this test with a battery charger connected to the unit battery.
N
No
otte
e:: All voltage readings should be taken between the chassis ground on the alternator and
the terminals indicated, unless stated otherwise.
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4.
Check that the resistor bypass fuse (F4) has been removed. Units with Thermo King
alternators must have the resistor bypass fuse (F4) removed.
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 and fuse F2 if used.
7.
Disconnect the alternator harness from the voltage regulator. On Thermo King alternators,
carefully push on the spring clip to release the plug lock.
8.
Turn the unit on, enter the Interface Board Test Mode, and energize the Alternator Excite
Output. Refer to the appropriate Diagnostic Manual for information about the Interface Board
Test Mode.
9.
Check the voltage at the sense circuit (2 circuit). Battery voltage should be present. If not,
check the sense circuit (2 circuit) in the alternator harness and the main wire harness, and
fuse F20 on the base controller.
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 alternator harness and the unified harness.
N
No
otte
e:: LED 18 lights up when the EXC circuit is energized. The EXC circuit is operated by a
Smart FET so during normal operation the unit must be running for the EXC circuit to
be energized.
11. Turn the unit off and reconnect the alternator harness.
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.
