What is a dual run capacitor?
A dual run capacitor is two run capacitors in one can, sharing a common terminal. It exists because a condensing unit has two motors to serve — the compressor and the condenser fan — and one can with three terminals is cheaper, smaller and one part to stock instead of two. The rating is written as two numbers: a 45+5 µF can carries a 45 µF section for the compressor and a 5 µF section for the fan.
Common questions
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Which terminal is which?
The can is stamped. HERM (for "hermetic", meaning the sealed compressor) takes the LARGER value and feeds the compressor. FAN takes the smaller value and feeds the condenser fan motor. C is common, and carries the line from the contactor to both sections. Photograph the wiring before you pull a single spade — HERM and FAN swapped will run the compressor on 5 µF, and it will not survive the summer.
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Can I replace a dual can with two single capacitors?
Electrically, yes — two singles wired to a shared common do exactly what the dual does, and it is a standard field fix when the right dual is not on the van. Practically you need somewhere to strap two cans inside a cabinet designed for one, and the reverse is not true: one dual cannot replace two singles whose values do not exist as a pair.
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Half of mine is dead. Do I replace the whole can?
Yes — you have no choice, and it is normal. The two sections share a housing, so a failed 5 µF section means a new can even though the 45 µF side still reads perfectly. This is the single most common capacitor failure in the trade: the fan section goes first because the fan motor cycles hardest.