Dometic 50/5 MFD AC Run Capacitor 3313107.018

When a Dometic 13,500 BTU rooftop air conditioner quits blowing cold, the run capacitor is one of the first parts we check. This is the Dometic 3313107.018, a dual run capacitor rated at 50/5 MFD, and it's the factory-spec part for those units. One case, two jobs. The 50 microfarad side feeds the compressor, and the 5 microfarad side keeps the fan motor turning. When it weakens, the whole unit struggles.

Here's what a tired capacitor looks like in the real world. You flip the AC on and hear a hum, but the compressor never kicks over. Or it starts, runs for a minute, then trips the breaker. Sometimes the fan spins slow or not at all. Those are classic signs the capacitor has lost capacitance, and on a hot afternoon in a closed-up rig or a boat cabin, it's the difference between comfortable and miserable. A run capacitor stores and releases the energy the motor windings need to get moving and hold a steady draw. Once it drifts out of spec, the motor pulls more amps, runs hotter, and eventually gives up.

This part is a direct replacement. It matches the original 50/5 MFD value, so you're not guessing at substitutions or stacking two separate capacitors to fake the dual rating. Match the value, wire it back the way it came off, and the unit pulls normal amps again. We always tell folks to snap a photo of the terminal connections before pulling the old one, because getting the compressor and fan leads back on the right posts matters.

A quick safety word, because it's important. Capacitors hold a charge even after the power is off. Before you touch the terminals, kill the breaker and the shore power, then discharge the old capacitor with an insulated screwdriver across the terminals. It's a two-second habit that keeps a stored jolt from surprising you. If you're not comfortable working around AC line voltage, this is a job worth handing to a tech.

On the water, we see a couple of things worth mentioning. Salt air is hard on capacitor terminals, so a dab of dielectric grease on the connections during install slows corrosion and keeps the contact clean. And on boats running off weaker shore power, a compressor that's slow to start puts extra strain on the capacitor. If your unit has always been a hard starter, a hard-start kit paired with a healthy capacitor takes the load off. Give the capacitor box some airflow too. Mounted next to a hot engine room or buried with no ventilation, any capacitor ages faster.

Fitment is straightforward. This 50/5 MFD value is the factory spec for Dometic 13,500 BTU rooftop air conditioners, the same platform used across a lot of RV and marine installs. If your unit calls for 50/5 MFD and uses Dometic part 3313107.018, this is your part. If you're not sure, pull your old capacitor and read the printed rating on the side before ordering. The value is stamped right on the can.

If you want to confirm the capacitor before you swap it, a multimeter with a capacitance setting reads it in seconds. Discharge it first, disconnect the leads, and check each section against its printed value. A good 50 microfarad section should read close to 50, and the 5 microfarad side close to 5. Anything well below that tells you the capacitor has drifted and it's time for a fresh one. It's the cheapest test in the toolbox, and it saves you chasing the wrong part.

It's a small part with a big job. A component that, when it fails, takes your whole air conditioner down with it. Keeping a spare in the parts bin isn't a bad idea if you spend real time off the grid or offshore, where a failed AC on a 100-degree day isn't just annoying. Replace it with the correct value, respect the stored charge, and your Dometic unit goes right back to cooling like it should.