motor wiring configuration
Figure 1. Motor wiring configuration.
In this month’s troubleshooting situation, our customer has called to say that the roof-mounted gas pack on their 1,500-square-foot home isn’t keeping them cool. Their specific description of the problem is that they “can’t feel any air” coming from the supply registers. When you arrive, you confirm that although the thermostat system switch is set in the cooling mode, and the fan switch is set in either the AUTO or On position, it doesn’t cause the indoor fan motor to operate. When you check the unit on the roof, you find:

• The condenser fan motor and compressor are running.

• The indoor fan motor is not running and is extremely hot.

• The TXV-fed indoor coil is clogged with ice.

Since you note that the wiring connections on the PSC-operated, three-speed fan motor (see the diagram in Figure 1 that shows the wiring configuration for this type of motor) are properly in place, you remove the appropriate cover to find the electrical components and main wiring harness connections. Among the components, you find a horizontally mounted run capacitor that has two orange wires connected to one terminal and one brown wire connected to the other terminal, and you note that oil has leaked from each terminal.

Disconnecting the power supply and checking with a meter, you note a reading of less than one microfarad when testing the capacitor.

Your troubleshooting questions:

1. Which component has failed?

2. Why did this failure cause the indoor coil to ice up?

Compare your answer with ours by clicking on the PDF link below.

Publication date: 9/9/2013

PDF - September Troubleshooting Answer

For information on Jim Johnson’s HVACR technician training DVDs, go to

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