Trane OA1D OA2D OA3D (Indirect Gas-Fired/Electric Heat) Manuel De Maintenance

OAU-SVX01E-EN

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within the proper tolerances, notify the power company to 
correct this situation before operating the unit.

Excessive three phase voltage imbalance between phases 
will cause motors to overheat and eventually fail. The 
maximum allowable voltage imbalance is 2.0 percent. 
Measure and record the voltage between phases 1, 2, and 
3 and calculate the amount of imbalance as follows:

V1, V2, V3 = Line Voltage Readings

VD = Line Voltage reading that deviates the farthest from 
the average voltage.

Example: If the voltage readings of the supply power 
measured 221, 230, and 227, the average volts would be:

VD (reading farthest from average) = 221

The percentage of Imbalance equals:

The 2.2 percent imbalance in this example exceeds the 
maximum allowable imbalance of 2.0 percent. This much 
imbalance between phases can equal as much as a 
20 percent current imbalance with a resulting increase in 
motor winding temperatures that will decrease motor life. 
If the voltage imbalance is over 2.0 percent, notify the 
proper agencies to correct the voltage problem before 
operating this equipment.

The compressor motor(s) and the supply fan motor are 
internally connected for the proper rotation when the 
incoming power supply is phased as A to L1, B to L2, and 
C to L3.

Proper electrical supply phasing can be quickly 
determined and corrected before starting the unit by using 
an instrument such as an Associated Research Model 45 
Phase Sequence Indicator and following these steps:

To prevent injury or death from electrocution, it is the 
responsibility of the technician to recognize this hazard 
and use extreme care when performing service 
procedures with the electrical power energized.

Each compressor shall be equipped with a crankcase 
heater. The proper operation of the crankcase heater is 
important to maintain an elevated compressor oil 
temperature during the “Off” cycle to reduce oil foaming 
during compressor starts. Oil foaming occurs when 
refrigerant condenses in the compressor and mixes with 
the oil. In lower ambient conditions, refrigerant migration 
to the compressor could increase.

When the compressor starts, the sudden reduction in 
crankcase pressure causes the liquid refrigerant to boil 
rapidly causing the oil to foam. This condition could 
damage compressor bearings due to reduced lubrication 
and could cause compressor mechanical failures.

% Voltage Imbalance = 100 X 

AV - VD

where;

AV

AV (Average Voltage) =

Volt 1 + Volt 2 + Volt 3

3

221 + 230 + 227

= 226 Avg.

3

100 X

226 - 221

= 2.2%

226



Turn off the main source feeding power to the unit 
field-supplied or factory-installed main disconnect 
device (switch or circuit breaker).



Close the unit disconnect device cover, leaving 
disconnect switch in the off position, and turn main 
source power on.



Observe the ABC and CBA phase indicator lights on 
the face of the sequencer. The ABC indicator light will 
glow if the phase is ABC. If the CBA indicator light 
glows, turn main source power off and then open the 
unit main disconnect device cover and reverse any 
two power wires.



Restore the main source power and recheck the 
phasing. If the phasing is correct, turn main source 
power off then open the unit main disconnect device 
cover, remove the phase sequence indicator, reinstall 
disconnect device cover and, leaving disconnect 
device in the off position, turn main power source to 
unit on.