Start Thermistors

Start thermistors are used to provide additional starting torque for PSC compressors. The start thermistor is a temperature sensitive device whose electrical resistance changes as a result o f a change in temperature. Positive temperature coefficient (PTC) thermistors increase their resistance with an increase in temperature. PTC thermistors are commonly used in the start circuit […]

Read More →

Motor Start Relay

The motor start relay is used to remove the starting capacitor from the motor starting circuit when the motor reaches about 75 to 80 percent of its operating speed. Start relays are made that can be actuated by either current or voltage. The start relays used with HVAC equipment motors are normally voltage-actuated relays (potential […]

Read More →

Motor Run/Start Capacitor Checks and Replacement

Run and start circuits on single-phase compressor motors use capacitors which affect the wattage, amperage draw, torque, speed, and efficiency o f the motor. Figure SP-9-10 shows typical run and start capacitors. Run capacitors are connected in the motor circuit at all times and are therefore referred to as continuous-duty capacitors. Older run capacitors are […]

Read More →

Electrical Considerations

Always be sure that the electric power source matches the motor power requirements. Check operating voltage, frequency, and phase. External field wiring to a motor should be done in accordance with the latest edition o f the National Electrical Code (NEC) and local code requirements. Operating voltages applied to compressor motors must be maintained within […]

Read More →

Electrical Motor Types

Both single-phase and three-phase motors are used in residential and light commercial system compressors. Permanent split capacitor (P SC ) and capacitor start-capacitor run (C SR ) motors are commonly used in single-phase hermetic compressors because of their good running characteristics and high efficiency. As shown in Figures SP-9-7 and SP-9-8, both the PSC and […]

Read More →

Compressor Electrical Problems

Grounded, Open, or Shorted Motor Hermetic motors are rugged and reliable but they can fail in several ways. A broken wire in a motor winding can prevent the motor from running. It can also fail due to an internal short circuit where one or more motor winding conductors short together or short to ground. Any […]

Read More →

Other System Problems that can Result in Compressor Failures

In addition to the failure modes previously described, there are several other system-related problems that, if not corrected, can result in the mechanical failure of a compressor. The major ones are listed here for consideration when troubleshooting compressors. Detailed coverage about the cause and effect of each of these system problems is beyond the scope […]

Read More →

Causes of Compressor Failures – Leaks

If a leak exists at the electrical terminals of a hermetic compressor (Figure SP-9-5), it cannot be repaired and the compressor must be replaced. If a leak exists at the girth weld or at the stubs, recover all refrigerant and repair the leak with silver brazing alloy. If the leak cannot be repaired, replace the […]

Read More →