Thermo King SGCO 3000, Manual

Page: 79 / 144

79
Electrical Maintenance
Battery
Inspect and clean the battery terminals, check the
electrolyte level during scheduled maintenance
inspections. The minimum specific gravity should
be 1.235. Add distilled water as necessary to
maintain the proper water level.
A dead or low battery can be the cause of an
ammeter indicating discharge due to lack of initial
excitation of the alternator.
NOTE: If the battery was discharged enough
that a boost was needed, the alternator may not
recharge the battery. This is because there may
not be adequate current to excite the alternator
field.
Relays
All the relays are 12 Vdc relays. The relays on the
microprocessor PC board are interchangeable.
The relays mounted on the inside of the control
box are interchangeable. The relays on the
microprocessor PC board are not interchangeable
with the relays mounted on the inside of the
control box. Test a relay by interchanging it with a
known good relay.
Fuel Pull Relay
The fuel pull relay (RL1) is located on the PC
board. It supplies power to the fuel solenoid
pull-in coil through the 8DP circuit. If the fuel
pull relay fails in the closed position, the fuel
solenoid pull-in coil will be damaged. If the relay
fails in the open position, the fuel solenoid will
not energize. The RL1 LED on the PC board will
light up when the fuel pull relay is energized.
Fuel Hold Relay
The fuel hold relay (RL2) is located on the PC
board. It supplies power to the fuel solenoid
hold-in coil through the 8D circuit. If the fuel hold
relay fails in the closed position, the unit would
operate continuously and not stop for a protection
shutdown. If the relay fails in the open position,
the fuel solenoid will energize momentarily but
will not stay energized. The RL2 LED on the PC
board will light up when the fuel hold relay is
energized.
Speed (Throttle) Solenoid Relay
The speed solenoid relay (RL3) is used on units
equipped with the EcoPower option and is located
on the PC board. It supplies power to the speed
solenoid through the 7D circuit. If the speed
solenoid relay fails in the closed position, the
engine would only run in high speed. If the relay
fails in the open position, the engine would only
run in low speed. The RL3 LED on the PC board
will light up when the speed solenoid relay is
energized.
CAUTION: Place the Unit On/Off switch
in the “OFF” position, Before connecting
or disconnecting the unit battery,
1. PC Board
2. Fuel Pull Relay (RL1)
3. Fuel Hold Relay (RL2)
4. Speed Solenoid Relay (EcoPower Option
Only)
Spare Relay (If Installed On Units Without
EcoPower Option)
5. Spare Relay (If Installed)
6. Terminal Boards
7. Start and Preheat Relays (RL5 and RL6)
Figure 39: Components Inside Control Box
1
7
2 3 5
6
4