Alternating Current Motors A to Z

Feb 18, 2026

Motor Minute™ Technical Tip – Alternating Current (AC) Motors A to Z

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 topic is alternating current motors A to Z.

Electric motors are built in different shapes, sizes and types to suit the application they are used in. Identifying the motor type will help properly service and, if needed, replace the motor.

This will be a very high-level introduction into the different types of electric motors used in HVACR and many other applications.

Electronically Commutated Motors (ECM) are used in the same direct drive applications as shaded pole and PSC motors. Due to their higher efficiency, they are displacing PSC motors in many applications. ECM motors do not use run or start capacitors. The motor is operated by a frequency drive and microprocessor built into the motor control. This motor control is buried inside the motor shell on watt rated motors but is visible on fractional horsepower (FHP) motors.

Split Phase Motors have moderate to low starting torque, high starting current and no capacitor. These motors are used on easy-to-start belt drive fans and blowers, as well as light-start pump applications.

Capacitor Start Induction Run (CSIR) Motors, also referred to as Capacitor Start or Cap Start, are designed for both moderate and high starting torque applications. They are used in fans, blowers, pumps, farm equipment and compressors. The start capacitor is visible on the outside of the motor in the “dog house”. When there is only one dog house on the motor, it’s typically a Capacitor Start Induction Run (CSIR) motor.

Capacitor Start/Capacitor Run (CSCR) Motors, also referred to as Cap Start Cap Run or Cap Start/Run, have higher starting torque and efficiency compared to capacitor start motors. They include a run capacitor (which stays in circuit) for higher efficiency and reduced running amperage. Generally, these motors are used for 1HP and larger single-phase applications similar to capacitor start. The run and start capacitors are visible on the outside of the motor in their respective “dog houses”. When there are two dog houses on the motor, it’s typically a Capacitor Start Capacitor Run (CSCR) motor.

Three-phase Motors have a high starting torque, high efficiency, and low current. They do not use a run or start capacitor and are suitable for larger commercial and industrial applications, including belt drive, direct drive and pumps.

There is obviously a lot more to learn about each of these motor types.

Being aware of the different types of motors, their physical characteristics and typical applications, is an essential building block to becoming a motor expert.

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.