Thermo King 920000, Manual

Page: 59 / 190

Electrical Maintenance
59
Unloading Timer (EUT)
The unloading timer energizes the unloading relay
(EUR) for approximately 20 seconds when the
engine or the electric motor is first started to
reduce the load. The unloading relay opens the
7K-7KU circuit, which supplies power to the
EXC terminal on the alternator.
This de-energizes the field coil, which keeps the
alternator from charging and allows the alternator
to turn freely. Disabling the alternator also
prevents the INDL circuit from energizing the fan
enable relays (FER and RFER). This keeps the
evaporator fan motors de-energized to reduce the
current draw on the battery while the alternator is
not charging. If the EUT is defective, it may be
difficult to start the engine or the electric motor.
Testing the Unloading Timer
1. Remove the CYCLE-SENTRY module from
the option board to prevent the Auto Start
system from preheating and cranking the
engine.
2. Disconnect the 20 wire from the engine reset
switch to prevent the engine reset switch from
tripping.
3. Place an On/Off switch in the Off position,
place the CYCLE-SENTRY switch in the
Cont Run position, and place the
Diesel/Electric switch in the Diesel position.
4. Disconnect the unloading timer wires (BLU
and ORG) from the main wire harness (ER
and 7KB) at the two pin connector.
5. Check the resistance between the ER wire in
the main wire harness and ground. If the
resistance is more than 90 ohms, check the ER
wire to the unloading relay, the unloading
relay coil and the CH circuit for bad
connections or opens.
4 3 2 1
5 6
1. Unloading Timer 4. Relay Tray
2. Option Board 5. Switch Panel
3. Circuit Breakers 6. Relay Board
Figure 19: Control Box Components