Split Phase Motor Windings

Split Phase Compressor Motor Windings

 There are many different types of motors used in the air conditioning, refrigeration and heating industry. Most of these motors perform many different application and most work by the principle of magnetic induction. Techs must gain an understanding of the following motors to successfully troubleshoot and work with them in the field: Split-Phase Motor, CS Motor, CSCR Motor, PSC Motor, Shaded-Pole Motor and the Three Phase Motor.

 The method of operation of each of these motors is similar but each serves a different purpose. All of these motors have an electrical winding or windings that are used to create the magnetic induction for motor operation. Split Phase Motors have medium starting torque and are normally used for operating fans in the fractional horsepower range. These motors have two motor windings, the start and the run winding which require help so to speak when starting and or running.

 These Motors are referred to as split-phase because a single power voltage supply is split between two individual windings, the RUN and the START. Both windings are used in the starting application of these motors, although once the motor reaches three fourths of its rated speed some means of removing the start winding from the circuit must be employed, such as a centrifugal switch.

 On start-up, voltage is applied to both the start and run windings of the motor which causes the motor to start to turn. Once the motor reaches 75% of its rated speed, the contacts of the centrifugal switch open, thus removing that start winding from the motor circuit. The starting torque and running efficiency of Split-Phase motors can be enhanced by the addition of a run or start capacitor, or perhaps both.




Run Capacitors increase the motors efficiency and are left in the motor circuit during operation. Run capacitors are wired parallel between the run and start winding of the motor as shown above.

 The start winding of the motor need not be removed from the motor circuit in this type of application because the run capacitor limits the amount of current draw through the start winding while it is in operation. Motors with run capacitors are called permanent split capacitor motors, or PSC Motors.

Split phase motor windings are simple and widely used.  They are always accompanied by a start and run capacitor. All though not always the case the capacitors can be dual in nature (meaning one capacitor 2 functions) or more commonly one capacitor for each and single start and run.  When needing a replacement part always make sure to document the proper voltage and microfarad.  This will insure that you get the right part because there are many different types that can cause damage if not properly replaced.