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Identifying PSC Replacement Motor

How to Identify the Correct PSC Replacement Motor

As a technician in the residential and light commercial HVAC (Heating, Ventilation and Air Conditioning) world, you will need to replace failed Permanent Split Capacitor (PSC) motors. When you need to find a suitable PSC motor replacement, following a few simple steps can make the process simple.

First, gather information about the motor. You will gather this information from a few different places:

  • The motor nameplate
  • Measuring the motor’s physical dimensions
  • Asking questions about the motor and how it was used

As you ask these questions, you will want to keep in mind the “Critical Three” elements of electric motors – application, characteristics and types. This will help to ensure you are selecting a replacement PSC motor that will be safe, reliable, and efficient.

It is recommended that a worksheet is used to write down the critical information as it is collected. The worksheet will make sure you don’t miss any critical information.

The Motor Nameplate

A typical PSC motor nameplate is located on the side of the motor shell. Since the nameplate is not always in legible condition, locating the information can be a bit intimidating at first. On the nameplate, you will find important product information including the motor manufacturer, model number, and catalog number.

What is the Motor’s Purpose?

In order to understand more about the application and the purpose of the motor, several questions should be asked:

  • What type of application did this motor come out of?
  • Is this motor exposed to outdoor conditions?
  • Are there any extreme temperature requirements?

When asking these questions, keep in mind that the motor might have failed because it was misapplied. It’s important to think about the application to prevent another failure in such a case.

Motor Nameplate Measurements

Details about these electrical characteristics can be found on the motor nameplate:

  • Voltage
  • RPM (Speeds)
  • Amperage
  • Phase
  • Horsepower (HP)
  • Service Factor (if one exists)
  • Frequency (Hz)

The motor nameplate also includes mechanical characteristics:

  • Enclosure (typically partially listed, but can also be determined by looking at the motor itself)
  • Frame Size
  • Thermal Protection (typically listed as “Thermally Protected”, which means the protection is automatic)
  • Bearing Type (not always listed)
  • Rotation (not always listed)
  • Insulation Class
  • Ambient Rating

Shaft dimensions are not typically listed on the motor nameplate. Instead, you will need to measure the shaft diameter and shaft length. A shaft diameter template is another option to simplify measuring the shaft dimensions.

The motor Mount is not usually listed on the nameplate either. If there is no obvious mounting type, you will need to ask about how the motor was mounted.

While the Type of Motor is not listed on the nameplate, the wiring diagram will show what type of motor it is.

PSC Motor Replacement Options

Now that we’ve gathered information from the nameplate, taken measurements, asked questions about the motor’s application and have recorded this information in our worksheet, we can look at correct replacement options.

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