TK 61552-2-MM-EN
45
–
Excessive current draw due to external devices when unit is powered down will result in
the LVD switch disconnecting the output after a short period of time (within hours -
depending on total current draw).
–
If current draw from all external devices exceeds 14 Amps the LVD will stop functioning
and require power cycling (disconnect and reconnect unit main battery terminals or plug
at LVD for longer than 10 seconds to hard reset).
Figure 13.
Cycle Power to Reset
Diagnosing the Low Voltage Disconnect (LVD)
If there is no power output from the LVD connection harness to external devices, Thermo King
recommends performing the following diagnostic steps:
1. Use multimeter/voltmeter to measure voltage output from LVD harness positive and negative
terminals (located in control box).
•
If voltage reading is much less (eg. 2 V or less) than the voltage reading of the main
battery, the LVD most likely requires a reset (when main battery voltage is less than 12.1
V).
2. Switch on unit (running).
•
When unit is running, the alternator will provide more than 13 V power output to LVD.
•
When LVD power input is 13 V or higher for 10+ seconds it should ‘unlock’ or reset the
LVD and provide power output to external devices once again.
N
No
otte
e:: Typical power output from alternator in normal unit running operation is 13.8 -
14.2V.
•
Once unit is running for 10+ seconds, perform step 1 again to confirm if issue is resolved.
Check that power output on LVD harness in control box is similar to main battery voltage
(12V or higher), and that external devices are now operating.
3. If Step 2 is unsuccessful, switch off unit and disconnect LVD harness plug from LVD (for 10+
seconds) and reconnect. Alternatively, disconnect main battery cable terminals for 10+
seconds and reconnect.
N
No
otte
e:: This action performs a power cycle (hard reset) of the LVD.
If this resolves the issue – root cause is likely one of the following:
•
High amp draw of 14+ Amps from all external device(s) which forced LVD to require hard
reset/power cycle.
•
Installation of external devices (such as third party telematics) sometimes require LVD to
be power cycled immediately after installation.
4. If none of the above steps resolves issue, root cause is likely to be:
•
Short circuit on LVD cables (from LVD to external devices/control box connection
harness).
•
Short circuit on LVD cables (from LVD to alternator).
•
Defective LVD.
If replacing the LVD resolves issue:
–
Check for any evidence of water ingress on the LVD plug terminals/pins on main
harness to LVD.
