Hvacr317 refrigeration
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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

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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 motors3

Split Phase Motors

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.

Centrifugal switch1

Centrifugal Switch

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.

Psc motor example

PSC Motor Example

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.

Cscr motor diagram

CSCR Motor Diagram

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 motor diagram

Hermetic Motor Diagram

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

Hermetic motors photo

Hermetic Motors Photo



  • 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

Shaded pole diagram

Shaded Pole Diagram

Cscr diagram

CSCR Diagram

Split phase diagram

Split Phase Diagram

Psc diagram

PSC Diagram

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