Once a capacitor is charged up, you might get a reading of zero until it discharges. Start capacitors have flat lids that the terminals are fastened to. If the top has bulged, it's an obvious sign the capacitor is bad.
CAUTION always discharge any stored voltage in a capacitor before working with it. Use an old screwdriver and short the terminals together to get rid of the possibly thousands of volts stored within! Most A/C units have capacitors that start the compressor and a separate circuit to start the fan.
Trying to restart a compressor too soon after it stops is a sure way to damage things. Pressures build up in the system and must have 5 minutes or more to equalize pressures so the compressor can start again. Most A/C units have a built in circuit that delays restarts.