Dual Run Capacitors

Motor Minute™ Technical Tip – Dual Run Capacitors

Hi, Chris from Regal Rexnord here with your Motor Minute technical tip. Helping you become an HVAC motor pro one minute at a time.

Today’s Motor Minute technical tip topic is “Dual Run Capacitors”.

Dual run capacitors are often utilized in A/C and heat pump outdoor units and package units to provide the run capacitor for both the Permanent Split Capacitor (PSC) outdoor fan motor and compressor.

The dual run capacitor is essentially two separate capacitors that share the same housing and the same line voltage terminal typically labeled (C) for common, meaning a shared terminal between both capacitors.

If the outdoor fan motor fails, the technician has a decision to make. Industry best practices recommend replacing the run capacitor anytime the motor is replaced. Does this mean the dual run capacitor needs to be replaced . . . or is there another option?

Replacing the dual run capacitor with the proper ratings for the compressor and the proper ratings for the new outdoor fan motor is one option.

Some might say that is an expensive capacitor to replace when only the fan side is in need of replacement. Others will point out that the new motor is getting the correct new capacitor, and the compressor is getting the value of upgrading to a new capacitor as well.

Then there is the challenge of stocking the numerous dual run capacitor ratings on the truck to prevent the need to drive to the supply house to get the proper ratings.

Another option is to leave the compressor connected to the existing dual run capacitor and install a new single run capacitor with the proper ratings for the new motor. This option may reduce the overall cost of the motor replacement and likely allow the job to be completed with a capacitor on the truck.

For this reason, many universal replacement PSC outdoor fan motors provide both connection options. The Century® 4-IN-1® motor is an example of a universal PSC outdoor fan motor with both of these options.

If the technician decides to replace the dual run capacitor, the 3-wire connection method shown below is used.

If the technician decides to install a new single rated capacitor for the new motor, the 4-wire connection method shown below is used. The existing dual run capacitor is left connected to the compressor.

Both options follow industry best practices. As a former technician, my process was based on a discussion with the customer about the merits of both options, so they can make an informed decision.

For more information on run capacitors and universal replacement outdoor fan motors with 3-wire and 4-wire connection options, please visit regalmmu.com and click on the Motor Minute™ icon to find these related tech tips:

• Run Capacitor Ratings And Replacement (July 14, 2021)
• How To Replace A Factory Installed PSC 3 Wire Outdoor Fan Motor With A Universal Motor (May 14, 2021)

And that’s a wrap on this segment of Motor Minute technical tips. Remember that we provide motor training and product information in multiple formats including videos, literature, podcasts, articles, of course Motor Minute technical tips and classroom education both online and face to face. All of this industry leading training is available at no charge to HVAC professionals at regalmmu.com. Thank you for taking the time to build your motor knowledge.