When replacing an HVAC capacitor, you must consider the following specifications:
Capacitance - The capacitance is a measurement of the amount of charge that the capacitor can store with a specified voltage applied. This is indicated by the microfarad rating (usually indicated by the units "uf" or “mfd”). When replacing a capacitor, the capacitance of the new run cap should be within 10% of the original one. If you are replacing a start capacitor, the capacitance of the new capacitor should not exceed 20% of the original one.
Voltage - Always select a replacement capacitor with the same or higher voltage as the original capacitor. One of the main causes of capacitor failure is incorrect voltage. For example, if you are replacing an HVAC capacitor rated for 370V, you can replace it with one that is rated for either 370V or 440V. However, you cannot replace a 440V capacitor with a 370V one.
Other specifications to consider
Case style - Capacitors can either be round or oval. As long as the capacitor fits within the mounting area and meets the appropriate specifications, its canister shape is irrelevant.
Ambient temperature - If you use your HVAC capacitor outside of its rated temperature range, it can cause the capacitor to fail. The wider the temperature range of your capacitor, the longer it will last.
Manufacturing tolerance - An HVAC capacitor will indicate its capacitance tolerance range, indicated by the "+/-" symbol (i.e. +/- 5%). This number is the maximum and minimum range of acceptable fluctuation of the rated capacitance in your HVAC capacitor.