Newmar King Aire – AC Capacitor & Fan Motor Service

The Newmar King Aire pulls its cooling load through a Dometic rooftop unit that was engineered for reliability, but like every AC system mounted that high and that exposed, it lives on borrowed time once the run capacitor starts to age. I’ve watched owners sit in 115-degree heat waiting weeks for a dealer service slot when a $60 part and thirty minutes of work could have had them back to full cold air by lunchtime. On this coach, two specific failures account for nearly every AC complaint I hear: a capacitor that quits without warning, and a fan motor that slows to a crawl or seizes altogether. Both are owner-fixable if you know what you’re looking at, and both respond to straightforward diagnostics and a handful of hand tools.

When the Dometic Capacitor Fails, Your Fan Goes Silent

A King Aire’s AC compressor will keep spinning and humming along, but the fan blade above it stays motionless—and that’s when you realize the capacitor has given up. This is the failure mode that catches most owners off guard, because the unit *sounds* like it’s trying to work. It’s also the most straightforward thing you can repair yourself, and the part costs almost nothing compared to a service call.

Parts and Tools

• Replacement dual run capacitor matched to the microfarad and voltage rating on the old one (typically 60/5 MFD for Dometic units) — check current price
• Replacement fan motor assembly if the existing motor is seized, burned, or produces no torque after capacitor replacement — check current price
• Needle-nose pliers for disconnecting spade terminals from capacitor leads
• Multimeter set to measure AC voltage and resistance
• Screwdriver set (Phillips and flathead) for removing access panels and motor mounting hardware
• Insulated wire strippers for preparing new connections if terminals are corroded
• Flashlight or headlamp for visibility inside the rooftop unit housing

Step-by-Step Instructions

Step 1: Kill power to the AC unit at the breaker

Locate your main 120V AC breaker panel inside the coach and switch off the breaker labeled for the rooftop air conditioner. Wait five minutes, then use a multimeter set to AC voltage to confirm zero volts at the unit’s power terminals. This prevents shock and protects the capacitor from discharging through your body. Do not skip this step—capacitors store electrical charge even when the unit is off.

Step 2: Access the rooftop unit and photograph the wiring layout

Climb onto the roof using a ladder and locate the Dometic unit’s access panel, typically a removable shroud held by four to six Phillips screws. Before disconnecting anything, photograph the spade terminal connections on the capacitor and motor leads from multiple angles. Note which wire connects to which terminal. This prevents confusion during reassembly and takes thirty seconds now versus ten minutes of troubleshooting later.

Step 3: Test the capacitor with a multimeter

Set your multimeter to resistance mode (ohms). Touch the probes to the two capacitor terminals. A good capacitor will show a brief needle deflection then return to infinity. A failed capacitor shows zero ohms or a steady resistance reading. If the reading is steady or zero, the capacitor has failed and needs replacement. If the meter shows infinity immediately, the capacitor is likely good and the problem lies with the motor.

Step 4: Disconnect and remove the failed capacitor

Using needle-nose pliers, carefully pull each spade terminal off the capacitor leads. Do not yank on the wires themselves—grip the terminal connector only. Once both terminals are free, note the capacitor’s microfarad and voltage rating printed on its body (usually 60/5 MFD, 370V). Remove any mounting bracket or clip holding the capacitor in place, then set it aside. Keep the old capacitor for reference when ordering the replacement.

Step 5: Install the new capacitor and reconnect terminals

Position the new capacitor in the same location and orientation as the original, securing it with the mounting bracket. Slide the spade terminals onto the capacitor leads, matching your photograph from step two. Push each terminal firmly until it seats completely—you should hear a small click or feel resistance. Tug gently on each wire to confirm the connection is solid and will not slip off during vibration.

Step 6: Test the fan motor for operation

Return to the coach interior and switch the AC breaker back on. Set the thermostat to cool mode and listen for the fan motor to engage within ten seconds. You should hear the motor torque up and feel air moving through the vents. If the fan remains silent or spins very slowly, the motor itself has failed and requires replacement following the same disconnection and terminal procedure as the capacitor.

Step 7: Verify cooling performance and secure the access panel

Allow the AC to run for ten minutes and check that cold air is flowing steadily through interior vents and that the thermostat is dropping the cabin temperature. Return to the roof and reinstall the access panel shroud, tightening all Phillips screws evenly. Do not over-tighten—snug is sufficient to prevent rattle and water intrusion. Confirm the breaker remains on and the unit cycles normally for at least thirty minutes before considering the job complete.

What works

• Exact factory specification match for your Dometic unit—no possibility of installing a capacitor with the wrong microfarad rating or voltage spec.
• The fan engages immediately when power cycles through after installation; you’ll feel the motor torque up and see cold air flowing through the vents inside fifteen minutes of completion.
• Premium-grade materials withstand the temperature swings and electrical stress that comes with living mounted on an RV roof, so you won’t be doing this job again in twelve months.

What doesn’t

• Stock levels on the big online retailers are unpredictable; budget three to five extra days for shipping even when you spring for the fast option.
• You have to safely discharge the old capacitor before touching it—shorting the terminals with an insulated screwdriver is non-negotiable, or you’ll take a shock hard enough to send you off the ladder.

I second-guessed the part choice the first time the fan motor still wouldn’t spin after swap, only to realize I hadn’t fully discharged the old capacitor and was working with a half-dead electrical system — operator error, not product failure. Order Fits for Dometic 3312195.000 Air Conditioner RV AC Motor Capacitor 60/5 MFD, Heavy Duty Air Conditioner Capacitor Replacement, Compatible with Dometic 3312195000 RV Air Conditioner Models and keep it on hand before you’re stranded in 115-degree heat.

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