Why All Systems Need a Start Capacitor


Eases the strain of compressor startup.


Extends the service life of your compressor.


Diminish/eliminate lights flickering upon system startup.

Your AC system works hard. Specifically, it’s your compressor that works so hard and consumes most of the power used. The compressor is like the heart of the system pumping refrigerant throughout the cycle. The driving force in the electrical supply is amperage. Think about the breakers in your home’s electrical panel; they may be 15 amp breakers up to possibly 60 amp breakers. If the circuit’s current rises above these number limits, the breaker will trip. However, tripping a standard breaker is not instantaneous. Your air conditioner upon startup could see a 150 amp spike (Locked Rotor Amps L.R.A.) for a few hundred milliseconds before it levels out to its normal running amperage (Run Load Amps R.L.A.) of 10 to 30 amps. This is due to the large amount of amperage that it takes to start a compressor from a stopped or “locked rotor” state.

This large spike of amperage generates a lot of heat, and heat is the enemy of all motors. Overtime, the heat will take its toll on the internal compressor windings and eventually kill the motor.

This is where a start capacitor comes in.

The start capacitor is a device connected to the compressor that stays in the circuit for a short time and creates a “phase shift” that dramatically shortens the time that the compressor draws that 150 amps, in turn generating much less heat. Another added bonus is it will greatly diminish/eliminate your lights dimming when the system starts up.

In a nutshell, the start capacitor allows the compressor to start up faster and generate less heat upon startup which will dramatically increase the service life.

Most manufacturers do not include start capacitors in their new equipment because even though it is an excellent component that adds to the longevity of the compressor, the equipment can run without it. Unfortunately, the manufacturers do not include them due to cost savings and other reasons which I’m sure you can imagine.

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