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HVACR317 - Refrigeration. Split Phase Motors PSC, CSIR, CSCR. Split Phase Motors. Split phase motors are also called induction start - induction run motors. These motors use a current relay or a centrifugal switch to remove the start winding from the circuit.

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Hvacr317 refrigeration

HVACR317 - Refrigeration

Split Phase Motors


Split phase motors
Split Phase Motors

  • Split phase motors are also called induction start - induction run motors.

  • These motors use a current relay or a centrifugal switch to remove the start winding from the circuit.

  • The start windings work on a phase shift principle.

Split phase motors1
Split Phase Motors

  • The voltage from the start winding to the run winding is 10 degrees out of phase.

  • Starting torque and running torque are relatively low in split phase motors because the phase shift is so low.

Split phase motors2
Split Phase Motors

  • These motors are used for belt drive blower applications such as small appliances like:

  • Washers

  • Dryers

  • Dish washers

  • Some older furnace blowers

Split phase motor
Split Phase Motor

  • The centrifugal switch removes the start winding from the motor circuit once the motor reaches around 75% of its rated speed.

  • This is the part that most often fails when a motor is started and stopped many times.

Centrifugal switch
Centrifugal Switch

  • The switch is normally closed when the motor is not operating.

Psc motors
PSC Motors

  • PSC stands for Permanent Split Capacitor Motors.

  • In order to increase the starting torque of a motor, you can insert a capacitor in series with the start winding circuit.

  • In a PSC motor, this capacitor remains in series while the motor is operating. There is no switch or relay that removes this capacitor from the circuit.

Psc motor
PSC Motor

  • Residential Condenser fan motors and residential furnace blower motors are the primary use of PSC motors.

  • PSC motors have moderate starting torque and intermediate running efficiency.

  • These motors are used primarily for small compressors and direct-drive blower and fan applications.

Csir motors
CSIR Motors

  • CSIR stands for Capacitor Start and Induction Run motors.

  • CSIR Motors use a start cap and a start relay.

  • Once the motor has reached 75% of its rated speed, the start capacitor is removed from the circuit.

Csir motors1
CSIR Motors

  • CSIR motors have a high starting torque and are used in residential and small commercial compressors.

  • May see them in beverage coolers or small reach-ins.

Cscr motors
CSCR Motors

  • CSCR stands for Capacitor Start Capacitor Run Motors. Can also be abbreviated to CSR (Capacitor Start and Run).

  • These are the same as Permanent Split Capacitor motors, except they have a start capacitor wired to them.

  • A start capacitor is a high capacitance capacitor that will provide the motor with additional torque when starting.

Cscr motors1
CSCR Motors

  • Once the motor has been started, the start capacitor must be taken out of the circuit using a switch or a relay.

  • These devices are called start components and will be covered in another section.

Hermetic motors
Hermetic Motors

  • Hermetic motors are single phase up to about 5 hp (horsepower).

  • Hermetic motors are those found inside the compressor shells.

  • They are wired the same way as any other split phase motor, but the start components must remain outside the compressor shell.

Hermetic motors1
Hermetic Motors

  • On the outside of the compressor shell there are three terminals. Most of the time these have some markings on them.

  • They are labeled C, R, S

  • S = Start winding

  • C = Common

  • R = Run Winding


  • If the windings are not marked, use your ohm meter and check resistance.

  • Check between all three windings.

  • The winding measurement with the highest resistance is between start and Run (S and R). The remaining terminal is Common ( or C).


  • Once you know C, check between C and the other two terminals.

  • The one with the highest resistance is Start (or S).

  • The one with the lower resistance is Run (or R).


  • The best way do this is to write down C, S, R in a triangle on a piece of paper and make sure you write down each measurement.

  • If you have any doubt - go back and do it again.

Motor speeds
Motor Speeds

  • Motor speeds are shown in RPMs (revolutions per minute).

  • This is a measure of how many times per minute the shaft rotates.

  • Sometimes you will need to figure out RPMs for a motor.

Motor speeds1
Motor Speeds

  • To figure motor speed, first use the motor labels.

  • If there is no label, use this formula:

    Speed (rpm) = (frequency x 120) / Poles