Dometic 3314471.017 RV AC Run Capacitor 55/15 MFD

When a Dometic air conditioner won't kick on, or the fan hums but the compressor never spins up, the run capacitor is the first part we check. This is the factory Dometic 3314471.017, a dual 55/15 MFD capacitor rated for 370 volts AC. It's the little metal can that stores and releases the jolt of energy your compressor and fan motor need to start turning and keep running smoothly.

The dual rating is what lets one part do two jobs. The 55 microfarad side feeds the compressor. The 15 microfarad side feeds the fan motor. So instead of two separate cans crowded into the AC chassis, Dometic built both into a single round housing with the terminals up top. Replace it once and both motors get the boost they need.

This capacitor is built for a long list of Dometic units. It fits the 640315, 641815, 641816, 641835, 641915, 641916, 641935, 651815, 651816, 651916, and 650015 series air conditioners. If you've got one of those cooling a cabin or a berth, this is your direct replacement. Same footprint, same ratings, no adapting and no guesswork.

These are the units you'll find cooling boats and RVs alike, from a single rooftop or under-bunk air handler up to the bigger ducted setups. The capacitor doesn't care what the unit is bolted to. What it cares about is the compressor and fan motor it's wired to, and those stay the same whether the AC is running off a dock pedestal, a generator, or an inverter.

Out on the water these units take a beating. Heat builds up in a tight equipment space, ventilation isn't always great, and after three to five seasons the 370 volt section is often the first thing to give out. We've seen it plenty on 30 to 40 foot sailboats and on trawlers running two Dometic units. One capacitor fails, cooling goes weak, and the second unit usually isn't far behind. So if you're already in there, it's worth carrying a spare.

How do you know the capacitor is the culprit? The classic signs are a compressor that hums but won't start, a breaker that trips a few seconds after the AC calls for cooling, weak or warm airflow, or a fan that turns slowly. A bulged or leaking top is a dead giveaway. None of those prove it on their own, but on a unit more than a few years old, a tired capacitor is the usual suspect and the cheapest thing to rule out first.

Size matters here too, because these older Dometic chassis are tight. The can measures 2-1/8 inches in diameter and stands 4-5/8 inches tall overall, with a body height of about 4-1/8 inches. On some units you can reach it once the shroud is off. On others you'll need to pull the whole AC chassis to get a hand on the bracket. Measure your space and check the diameter before you order, because a capacitor that's a hair too wide won't seat in the clamp.

Swapping it is a straightforward job for anyone comfortable around AC wiring, but respect the charge. A capacitor holds voltage even after the power is off, so discharge it across a resistor or an insulated screwdriver before you touch the terminals. Note where each wire lands before you pull them. This one isn't polarized, so there's no positive or negative to sort out, but the common, compressor, and fan terminals each feed a specific circuit and the wiring has to go back exactly the way it came off. Match the 55/15 MFD and 370 volt ratings when you replace it, and don't substitute a different microfarad value to make another part fit.

This is a service part, plain and simple. It's the capacitor only, with no wiring harness and no hard-start kit in the box. If your compressor is getting up there in years and struggles on generator power, pairing a new capacitor with a separate hard-start kit can cut the inrush. For most owners, though, dropping in the correct Dometic capacitor is what gets the cold air flowing again.