How to Find Common, Start, and Run on a PSC Compressor Motor

As an HVAC technician, understanding how to find common, start, and run on a PSC (Permanent Split Capacitor) compressor motor is crucial for troubleshooting and maintenance. Here’s a step-by-step guide to help you identify these terminals:

Step 1: Safety Precautions

Before starting, ensure that the power to the compressor is turned off to prevent any electrical hazards.

Step 2: Set Multimeter

Set your multimeter to the ohms setting. Ensure that the probes are not touching, so the multimeter reads “OL” (open loop).

Step 3: Testing Resistance

  • Test each terminal of the compressor motor by placing the multimeter probes on the terminals.
  • Record the resistance values for each pair of terminals.

Step 4: Identifying Terminals

  • The terminal with the highest resistance reading is the common terminal.
  • The terminal with the second-highest resistance reading is the start terminal.
  • The terminal with the lowest resistance reading is the run terminal.

Step 5: Understanding the Readings

  • The common terminal is where both windings connect, resulting in the highest resistance.
  • The start terminal has the second-highest resistance and is connected to the start winding.
  • The run terminal has the lowest resistance and is connected to the run winding.

Step 6: Verification

To verify your findings, cross-reference the identified terminals with the compressor motor’s wiring diagram.

By following these steps, you can accurately identify the common, start, and run terminals on a PSC compressor motor, enabling you to perform effective troubleshooting and maintenance.

Remember, safety should always be a priority when working with electrical components. If you are unsure or uncomfortable with these procedures, it’s best to consult a qualified HVAC professional.

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