When your HVAC system needs a new capacitor, the first question is always: single or dual?

Single Run Capacitor A single run capacitor hooks up to a single motor and is more commonly used in smaller HVAC systems, like small air conditioners. It has two terminals and handles one job — keeping one motor running steadily. National Air Warehouse

Dual Run Capacitor A dual run capacitor combines two capacitors in a single unit, typically serving both the compressor and the fan motor in air conditioning systems. It features three terminals instead of two, allowing it to connect to and assist two different motors — making installation and maintenance easier. Blikai

Why most modern systems use dual run: Space inside a condenser unit is tight. Dual run capacitors simplify wiring and save space, which is important in heat pumps and condensers. The three-terminal design lets you use one part instead of two separate capacitors. ODG Electronics

Understanding the numbers: The ratings printed on the capacitor (e.g. 40+5 MFD, 440 VAC) tell you everything. The first number is the compressor capacitance, the second is the fan capacitance, and the VAC rating is the voltage. A 440-volt dual capacitor can replace a 370-volt one, but not the other way around. Always keep the capacitance within 5% of the original value. ODG Electronics

Check your old capacitor’s label for the µF and VAC values, count the terminals (2 = single, 3 = dual), and match those specs exactly when ordering a replacement.