Dometic 55/5 MFD 370V AC Run Capacitor 3313107.036

If your Dometic high-efficiency rooftop air conditioner won't kick on, hums but doesn't start, or the fan spins slow while the compressor sits dead, the run capacitor is the first part to check. This is the factory Dometic replacement, part number 3313107.036, a dual run capacitor rated 55/5 MFD at 370 volts AC. It's the same size and rating the unit shipped with, so you're not guessing at fitment.

Here's what the 55/5 rating actually means. This is a dual capacitor, so it does two jobs in one can. The 55 microfarad side feeds the compressor motor, the big draw that does the cooling. The 5 microfarad side runs the fan motor that moves air across the coils. One part, two circuits. That's why a single bad capacitor can leave you with a compressor that won't start and a fan that barely turns, or any combination in between.

Capacitors are the most common failure point on an RV rooftop AC, and they don't always fail dramatically. Sometimes the top bulges. Sometimes it looks fine and just quietly loses capacitance until the compressor can't get the kick it needs to start. When that happens you'll often hear a low hum followed by the breaker tripping, or the compressor cycling on the thermal overload every few minutes. Swapping the capacitor is usually a fifteen-minute fix and a fraction of the cost of a service call.

The physical size matters as much as the electrical rating. This one measures 4-1/4 inches tall and 2-1/2 inches in diameter, sized to drop into the capacitor bracket inside a Dometic high-efficiency unit without fighting the cover. Before you order, pop the shroud and confirm your old cap reads 55/5 MFD 370V on the data label. Ratings vary across BTU sizes, and putting the wrong microfarad value in will run the motors hot.

A word on the wiring, because this trips people up. The terminals are marked, typically HERM for the compressor, FAN for the fan, and C for common. Before you pull a single wire, snap a photo or label each lead. Get them crossed and the motors won't run right. And always discharge the old capacitor across a resistor or an insulated screwdriver before you touch the terminals. These hold a charge even with the power off, and 370 volts stored in a can will get your attention.

Not sure the capacitor is your problem? A cheap multimeter with a capacitance setting will tell you fast. Disconnect power, discharge the cap, pull the leads, and read each side. The 55 microfarad terminal should read close to 55, and the 5 microfarad side close to 5. If either side reads low, open, or shorted, replace it. A capacitor that measures fine while the AC still won't start points you toward the motor or the control board instead, so you're not throwing money at the wrong part.

The 370 volt AC rating is the working voltage the capacitor is built to handle continuously, and it's the correct spec for these Dometic units. Heat is what ages a capacitor fastest, so if you run in consistently high ambient temperatures, keep an eye on service life. Mount it back in its bracket so it isn't rattling loose, and it'll give you seasons of reliable starts.

This replacement suits first-time owners and seasoned techs alike. If you've never opened up a rooftop unit, the job is approachable as long as you kill the breaker, discharge the old cap, and label your wires. If you do your own service every spring, keeping one of these on the shelf means a dead AC on a hot afternoon is a quick swap instead of a lost weekend. Bottom line, if you've diagnosed a weak or failed capacitor on your Dometic high-efficiency air conditioner, this is the exact-match part. Right microfarad, right voltage, right size. Get it in, get your air back on.