Turn off power to the AC unit at the breaker
Discharge the capacitor safely with an insulated resistor or insulated screwdriver rated for the task
Remove the access panel
Take a photo of the wire connections
Label and disconnect the wires from the capacitor terminals
Set the multimeter to capacitance mode
Place the multimeter probes on the capacitor terminals
Read the capacitance value on the meter
Compare the reading to the capacitor’s rated value printed on the case
Replace the capacitor if the reading is far below or above the rated value
If your multimeter has no capacitance mode, set it to ohms
Touch the probes to the terminals and watch for the reading to start low and rise toward infinity
Reverse the probes and repeat the test
Replace the capacitor if the reading stays at zero, stays at infinity, or does not change
Reconnect the wires exactly as labeled
Reinstall the access panel
Restore power to the unit