Electrical Maintenance 8-24
PHASE CORRECTION OPTION
Phase correction is a system that automatically adjusts the phase sequence of the power supply to correspond with the wiring of
the electric motor. The main components of the system are the phase sensing module (PSM), two relays, and the two motor
contactors (MC1 and MC2). Contactor MC1 is wired to retain the phase sequence. Contactor MC2 is wired to change the phase
sequence. The phase sensing module senses the phase sequence at the heater contactor and energises the appropriate motor
contactor by energizing one of the relays.
The electric disconnect relay (EDR) is energised by the phase sensing module when ac voltage is detected on L1, L2 and L3.
When the electric relay is energised, it enables the dc segment of the unit’s electrical system.
Diagnosing the Phase Correction System
If the electric motor operates backwards (unit airflow incorrect):
Turn the electric power supply OFF. Refer to the appropriate diagnostic’s manuals and wiring/schematics diagrams.
If the electric motor does not operate at all:
1. Make sure that the unit is turned ON, the Diesel-Electric switch is in the ELECTRIC position, and that the power supply is
connected and turned ON.
2. Check for battery voltage (12 Vdc) at the terminal strip in the high voltage tray.
a. Battery voltage should be present at the 8 terminal. If not, check the 8 circuit, reset switch, control circuit breaker, On-Off
switch, 2A circuit, 2 circuit fuse link and battery.
b.Battery voltage should be present at the 8E terminal. If not, check the 8E circuit and the Diesel-Electric switch.
c. Battery voltage should be present at the 8A terminal. If not, check the EDR relay .
Typical High Voltage Tray – SL and SLe
1. Heater Contactor
2. Motor Contactor - MC1
3. Motor Contactor - MC2*
4. Phase Indicator Module;
or Phase Sensing Module (PSM)*
5. PSM Relays (2)*
6. Overload Relay
*Auto Phase Option Only
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