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62-11175 COMFORTPRO SERVICE MANUAL
3-15
3.9.4 Potential Relay Theory
In a Capacitor Start, Capacitor Run compressor the start capacitor is only designed for
momentary use. The Potential Relay (NC) is used to connect and disconnect the start
capacitor from the compressors start windings. Induced Voltage is generated in the start
winding when of the compressor when it is running. The voltage induced in to the start
winding is a function of the speed of the rotor and the magnetic field that is generated.
When the compressor is first energized, the voltage in the start windings is less than the
line voltage (120 VAC). As the compressor speed (RPM) increases, the voltage in the
start windings increases significantly higher than the line voltage (up to 275 Volts) until
full compressor speed (RPM) is reached.
The Potential Relay's coil is connected across the start windings, and is designed to
respond to the increase of voltage as the compressor's speed increases. The normally
closed Potential relay contacts are designed to open at a 75% of the full compressor
speed (RPM). The Start Capacitor is connected to the relay contacts so when the relay
opens (75% of the full compressor speed RPM) the start capacitor is disconnected from
the system.
3.9.5 Alternator Troubleshooting
1 Unit switched OFF, harness connected
Check alternator feedback wire (brown) at the alternator for 5 volts.
If 5 volts are not found disconnect 'T' connector from alternator and retest. If 5 volts are
found the alternator is faulty.
If 0 volt is found check alternator feedback wire (brown) for open, and power (B+) and ground
(B-) to APU controller and repair as required. If no fault is found the APU controller is faulty.
2 Unit switched ON (glowing), harness connected
Check alternator field power wire (purple) for 12 volts. If 0 volt is found check alternator
field power wire (purple) for open and power (B+) and ground (B-) to APU controller and
repair as required. If no fault found the APU controller is faulty.
Check alternator feedback wire (brown) at alternator for 0 volt. If 5 volts are found the
alternator is faulty.
3 Unit running, harness connected
Check alternator feedback wire (brown) at alternator for 5 volt. If 0 volts are found the
alternator is faulty.
4 Unit running, then stops
Check alternator jumper harness (red) at alternator connection for 12.5-14.1 volts.
If 16-17 volts is found, check for alternator jumper (red) open and replace as required.