Newmar King Aire – AC Capacitor & Fan Motor Service

Newmar King Aire – AC Capacitor & Fan Motor Service

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Complete repair guide for the Newmar King Aire – AC Capacitor & Fan Motor Service. Follow these steps to diagnose and fix the issue yourself.

Parts & Tools You’ll Need

Step 1: Diagnose AC System & Disconnect Power

Start by switching off your RV’s main electrical breaker and the dedicated AC disconnect switch on the roof—you’ll need to kill all power to the unit before touching any components. Use a non-contact infrared thermometer to record the current air temperature output from your AC vents; if readings are above 60°F or the system won’t cool, you likely have a failed capacitor or fan motor. Take photos of your existing capacitor’s microfarad (µF) rating and voltage (typically 370V or 440V on dual-run units) before removal, as you’ll need to match these specs exactly when ordering a replacement.

Step 2: Remove Rooftop AC Shroud & Access Interior

Locate the four to six fasteners holding your King Aire’s rooftop AC shroud in place—these are typically 1/4-inch hex bolts around the perimeter. Carefully lift the shroud straight up and set it aside on a clean surface; note the position of any wiring harnesses connected to the thermostat/control board so you can reinstall them correctly. Take this opportunity to inspect the AC roof gasket for cracks, deterioration, or gaps; if the gasket is compressed or damaged, you’ll want to replace it with a new AC roof gasket & self-leveling sealant to prevent future water leaks.

Step 3: Test & Remove Faulty Capacitor

Before touching the capacitor, use an insulated screwdriver to short the terminals together (this safely discharges any residual electrical charge)—this step is critical for your safety. Locate the dual-run capacitor mounted near the fan motor; it’s usually a cylindrical or oval component with two or three terminals labeled C, HERM, and FAN. Use a photo or diagram to document terminal connections, then carefully disconnect the spade connectors and unscrew the mounting bracket to remove the old capacitor.

Step 4: Install New RV AC Dual Run Capacitor

Position your new RV AC dual run capacitor into the mounting bracket, ensuring it sits securely and won’t vibrate against other components during operation. Reconnect the spade terminals to their original positions (HERM, FAN, and C)—misalignment here will prevent your AC from running or cause immediate failure. Double-check that the capacitor’s microfarad and voltage ratings match your documentation from Step 1; Dometic and Coleman-Mach units typically use 35/5 µF at 370V ratings.

Step 5: Inspect & Replace Fan Motor If Needed

Spin the fan motor shaft by hand to check for smooth rotation and bearing play—if it’s stiff, grinding, or won’t turn freely, the motor needs replacement. If replacing, disconnect the three-wire harness from the motor and remove the three mounting bolts holding the motor to the AC shroud assembly. Install the new RV rooftop AC fan motor in reverse order, ensuring the wire connectors are fully seated and the motor spins freely before reassembly.

Step 6: Clean Coils & Reseal Gasket

With the shroud removed, spray your AC evaporator/condenser coil cleaner foam across the coil fins—let it sit for 3–5 minutes, then rinse thoroughly with a garden hose set to low pressure. Use a fin comb/coil straightener tool to gently straighten any bent fins that restrict airflow; bent fins reduce cooling efficiency by up to 15 percent. Before reinstalling the shroud, remove the old AC roof gasket completely and apply the new AC roof gasket & self-leveling sealant around the mounting surface to prevent water intrusion.

Step 7: Test System & Verify Cooling Performance

Restore power by flipping the main electrical breaker and AC disconnect switch, then set your thermostat to the coldest setting and run the AC for 10–15 minutes. Use your non-contact infrared thermometer to measure the supply air temperature at the vents—you should see readings between 42°F and 55°F; anything warmer indicates a problem with the new capacitor or motor installation. Listen for unusual grinding, squealing, or rattling noises; if present, shut down immediately and recheck motor alignment and capacitor terminal connections.