Learn How To Test A Start Capacitor.

Asked By 0 points N/A Posted on -

Hi. I have a faulty electric motor, and it won’t start due to a problem in the start capacitor. Could you please explain how to test a start capacitor? Thanks!

Answered By 1050 points N/A #88213

Learn How To Test A Start Capacitor.


A start capacitor is very common in home appliances and all HVAC devices. The only function of a start capacitor is to bring the motor up to a predestined speed by increasing the starting torque of the motor briefly, after which it comes out of the circuit. It is mostly controlled by a centrifugal switch. If the switch is always ‘open’ then the capacitor stays out of the circuit preventing the motor from starting. Also, if the switch is always ‘closed’, the capacitor never disconnects and shorts. You were right to judge that the motor isn’t starting due to a faulty start capacitor.

The following steps show a way to test if your start capacitor is still working or is dead. Preliminarily, if you notice any bulging at the top of the capacitor or deposition of a dark fluid, then your capacitor is dead.

1. Discharge the capacitor A capacitor stores electric charge in it. So it is essential to remove any residual charge from it at the beginning. The simplest way to do this is to connect the capacitor terminals to a low voltage device such as a 20-watt bulb.

2. Use a voltmeter Set the voltmeter to 1k ohms. Touch the leads of the voltmeter to the capacitor terminals and then touch them again reversing the leads this time. For a working capacitor, the needle (analogue voltmeter) will swing from 0 ohms to infinity, or show an open line (digital voltmeter) each time you reverse the leads. There will be no effect if the capacitor is not working.

3. Use a Multimeter Alternatively, if you have a multimeter, you can check the capacitance. If the reading is close to the one mentioned on the capacitor, then it is not faulty.

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