The best way to test a condenser (capacitor) is with a condenser tester. But.....most guys don't have one of those, so the easiest way then to test a condenser is with an analog multi-meter that has a moving needle and an "ohms" setting.
Here is the standard explanation on how to test a condenser with a multi-meter:
1.) Remove the condenser from the engine (or at least disconnect the lead wire). Note the small metal connector located on the end of the condenser. This connector is the "hot" or power connection. The metal case of the condenser is the grounding point. Discharge the condenser by shorting the lead wire on the condenser to the metal condenser case.
2.) Switch the analog multi-meter to the ohms position. Place the red lead for the meter into the "ohm" connector on the meter. Insert the black lead for the meter into the "com" or common connector on the meter. Set the resistance range to the highest available setting (if it is selectable). Connect the meter test leads together and zero the meter with the "ohms adjust" knob. If the meter won't zero replace the battery in the meter. (Yes, an ohm meter has a battery).
3.) Touch the red lead on the meter to the hot connector on the condenser. Place the black lead on the meter to the metal case on the condenser. The meter's needle should jump slightly to the right on the scale (toward 0-ohms), then should drop back to the left towards infinite resistance. Hold the leads in place for 15 to 20 seconds. This action places charge in the condenser. If the test shows any reading other than infinity, the condenser is leaking and needs to be replaced.
4.) Remove the leads from the condenser and reverse the placement to the condenser. Move the red lead from the hot connector on the condenser to the metal case on the condenser, and move the black lead from the metal case on the condenser to the hot connector on the condenser. At the moment where both leads are touching the correct points, the meter needle should jump towards the right on the scale. The second time the needle may move twice as far, as this action discharges the condenser. Holding the leads in contact should again result in movement of the needle back toward infinite resistance.
5.) Movement of the meter's needle indicates the condenser is good. If no movement was indicated on the meter in any circumstance, the condenser is bad and must be replaced. Retest the condenser several times for a consistent reading.
