How to Troubleshoot an Electric Motor Capacitor Problem

Utilize a digital multimeter to troubleshoot motor capacitor problems.
••• Polka Dot Images/Polka Dot/Getty Images

A bad motor capacitor may cause starting problems or could shut off the motor while running. Motor capacitors store electrical energy for the motor to use. The higher the capacitance of the capacitor the more energy it can store. A damaged or burnt out capacitor may hold only a fraction of the energy needed for the motor if its capacitance is low. A capacitor consists of two metal, parallel plates encased within a plastic exterior. Capacitance is measured in microfarads.

    Turn off the power to the motor then disconnect it from the power source. Inspect the motor capacitor. If it is not attached to the motor at two points it needs to be replaced. Also, if the capacitor is visibly cracked it should be replaced.

    Attach the red (positive) alligator clip of the multimeter to the positive lead of the motor capacitor.

    Attach the black (negative) alligator clip of the multimeter to the negative lead of the motor capacitor.

    Turn the dial on the multimeter to the microfarad capacitance setting. This is labeled by the lowercase Greek letter "µ" — pronounced as "mu" — followed by the letter "f." If you have an auto-ranging multimeter it will do this step for you automatically. Just set the multimeter on capacitance in that case labeled "f" for farad.

    Turn on the digital multimeter. The reading on the screen is the capacitance of the capacitor in microfarads. If this is not the value written on the motor capacitor's case it requires replacement.

Related Articles

How to Size a Capacitor to an Electric Motor
How to Charge High Voltage Capacitors
How to Calculate Ohms to Microfarads
Can You Repair a Burned-Out Electric Motor?
How to Troubleshoot Single Phase Motors
How to Reduce 12 Volt to 6 Volt
How to Calculate Potential Difference
How to Calculate Motor Inrush Current
How to Calculate Power Rating
How to Test a Ford 9N Ignition Coil
How to Test a Blower Resistor
How to Charge a 12V Battery With a DC Motor
How to Calculate Motor Efficiency
How to Find a Short in a Circuit Board
How to Learn to Read Surface Mount Capacitors
How to Rewire an Electrical Motor to Generate AC Current
How to Test DC Motors
How to Calculate Induced Armature Voltage
How to Measure the Ohm Value for an Inductor
How to Convert 12 Volt Alternator to 120 Volts