<P> A motor capacitor, such as a start capacitor or run capacitor (including a dual run capacitor) is an electrical capacitor that alters the current to one or more windings of a single phase AC induction motor to create a rotating magnetic field . There are two common types of motor capacitors, run capacitors and start capacitors . The units of capacitance are labeled in microfarads (μF). Older capacitors may be labeled with the obsolete terms "mfd" or "MFD", which means microfarad . </P> <P> Motor capacitors are used with air conditioners, hot tub / jacuzzi spa pumps, powered gates, large fans or forced - air heat furnaces for example . A "dual run capacitor" is used in some air conditioner compressor units, to boost both the fan and compressor motors . </P> <P> Start capacitors briefly increase motor starting torque and allow a motor to be cycled on and off rapidly . A start capacitor stays in the circuit long enough to rapidly bring the motor up to a predetermined speed, which is usually about 75% of the full speed, and is then taken out of the circuit, often by a centrifugal switch that releases at that speed . Afterward the motor works more efficiently with a run capacitor . </P> <P> Start capacitors have ratings above 70 μF, with four major voltage classifications: 125 V, 165 V, 250 V, and 330 V. Examples of motor capacitors are: a 35 μF, at 370 V, run capacitor, or an 88--108 μF at 250 V start capacitor . </P>

What is the purpose of a start capacitor
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