Electrical Maintenance 8-23
EVAPORATOR HEATERS
(If So Equipped)
Test the resistance of each evaporator heater by disconnecting it from the circuit. Check resistance with an ohmmeter.
SL, SLE, SLX, SLXe, SLXi
The resistance of each heater should be 115 to 140 ohms.
AC COMPONENTS (MODEL 50 UNITS)
NOTE: The unit uses high voltage alternating current (ac) during electric operation. Lethal voltage potentials can exist on
connections in the high voltage box. Take appropriate precautions and use extreme care when testing the unit.
Electrical Contacts
Inspect all relay contacts for pitting or corrosion during scheduled maintenance inspections and repair or replace as necessary.
Test the contact points of the contactor by checking the voltage drop across each set of points when the contactor is energised
and the system is operating. If the voltage drop is more than 15 Vac, replace the contact points as a set.
Test the contactor coil by checking the voltage across the coil. The contactor coil should be energised by a minimum of 10 Vdc.
Overload Relay
The overload relay should open if the motor circuit current draw is more than 20 amperes at 380-460 Vac. The overload relay
should open the motor circuit if the current draw is more than 40 amperes at 200-230 Vac.
Phase Indicator
Standard TG-VI model 50 units are equipped with a phase indicator light. This light comes on when the phase of the power supply
is incorrect. Incorrect phase causes the electric motor to spin backwards, which causes the unit’s fans to spin backwards. (MT
µP-IV, µP-V, µP-VI , SR-2 and SR-3 have automatic phase correction).
If the phase indicator light comes on when the unit is connected to an electric power supply, the phase of the power supply must
be corrected. Turn the power off and switch the positions of any two of the power leads in the power cable plug. DO NOT disturb
the green ground wire. This procedure should be performed by a qualified electrical technician.
If the electric motor spins backwards (unit airflow incorrect), but the phase indicator light does not come on:
1. Turn the electric power supply off and check the unit wiring.
a. Wires from the phase indicator module should be connected to the heater contactor terminals as follows: BRN to L1, BLU
to L2, and RED to L3.
b.Wires L1, L2, and L3 should be connected respectively to terminals L1, L2, and L3 on the heater contactor and the motor
contactor.
c. Wires L1, L2, and L3 should be connected respectively to terminals X, Y, and Z in the power receptacle.
2. Disconnect the BLK wires from the phase indicator light, turn the power supply ON, and check the voltage between the two
BLK wires coming from the phase indicator module.
Voltage of approximately 120 volts ac indicates that phase indicator module is acceptable and that the light is probably
defective.
No voltage indicates that the phase indicator module is probably defective if the wiring is correct and the power supply phase
is incorrect.
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