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One of the most important products in the Heating, Ventilation and Air Conditioning (HVAC) industry is the electric motor. This is the basic component of all HVAC solutions, powering blowers to move air. Electric motors drive compressors for refrigerants and power pumps as well as chilled and hot water applications.

AC motors used in hvac applicationsThe type of motor that is used in a HVAC system depends on its application. Electric blowers or propeller fans, for example, usually require motors that have a low starting torque, while compressors require motors that have high starting torque. This is why it is important for HVAC engineers to select the appropriate motor for the job – the use of the incorrect motor will result in problems throughout the operation of the HVAC system.

Split phase motors are known as the workhorse of the HVAC industry. Usually used in air conditioners because these motors provide high starting torque, there are two common types of split phase motors.

Capacitor start motors make use of a start capacitor to boost their starting torque. Most of these motors use a centrifugal switch to disconnect the start capacitor from the start winding circuit at the time the motor will reach around 70 to 80 of its run speed. The resistance-start-induction-run electric motor, on the other hand, has a start winding and a run winding. The two windings are out of phase by 45 to 90 degrees which gives the motor a boost on start-up. Unlike the capacitor-start-induction-run motor that uses a capacitor, this motor makes use of a centrifugal switch to drop the start winding out of the circuit.

Permanent Split Capacitor (PSC) electric motors are used for many refrigeration and air conditioning compressor applications. These motors are single phase electric motors. They are easily reversible from the clockwise to counter-clockwise direction. The PSC motor uses a capacitor and has good running efficiency. When a PSC motor is used in compressors, it makes use of two capacitors attached to its wiring. The first one serves as a start capacitor to boost the starting torque, and the second is a run capacitor to increase its running efficiency.

Shaded-pole electric motors are usually only used for application fractional horsepower applications wherein the start and run torque requirements are minimal. These motors are used in devices with low starting torque such as electric fans and small pumps. Shaded-pole electric motors do not use capacitors and are not easily reversible.

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