To determine if the capacitor is grounded, touch the ohmmeter probe between the metal case and each terminal in succession. You will measure zero resistance from a grounded capacitor. When replacing capacitors, always try to find a replacement with the same value as measured in mfd's. If the appropriate replacement is not available, however, you can add the value of two capacitors by wiring them in parallel. The reason is that using two capacitors in parallel increases the thermal capacity of the capacitor because the greatest surface area of the two units increases the capacitor's ability to dissipate heat.
Capacitors also have voltage ratings.
This relates to the maximum voltage the capacitor can stand across its terminals, and is determined by the strength of the dielectric. When making replacements, it's acceptable practice to use capacitors with higher voltage ratings than the original unit. It also is generally acceptable to use a replacement capacitor that is one standard rating size higher than the original as a temporary solution in the field. But if you make such a substitution, always check to make sure the output amps do not exceed the motor's nameplate amps. Some technicians discharge the capacitor by placing a tool, such as a screwdriver, across the terminals.