When you boondock regularly — no hookups, no campground services, no one nearby to help — you develop a different relationship with your rig’s systems than a weekend camper does. Everything has to work. You learn the failure modes, the warning signs, and the repairs before you need them, not during. On a Rockwood or Flagstaff, the rooftop AC unit is one of the first things to show its age, and it almost never fails in spring — it fails on the hottest day of July, in the middle of the desert, when you’re already sweating through your shirt before noon. Nine times out of ten, the culprit is a worn run capacitor or a failing fan motor — two components that are cheap to replace, straightforward to diagnose, and absolutely worth understanding before you’re staring at a dead unit 40 miles from the nearest parts store.
Parts & Tools You’ll Need
- RV AC dual run capacitor (Dometic/Coleman-Mach)
- Rooftop AC fan motor
- RV AC thermostat / control board
- AC evaporator/condenser coil cleaner foam
- Rooftop AC shroud / outer cover
- AC roof gasket & self-leveling lap sealant
- Fin comb / coil straightener tool
- Non-contact infrared thermometer
Disclosure: This post contains affiliate links. We may earn a commission on qualifying purchases at no extra cost to you.
Step-by-Step Repair Guide
Step 1: Diagnose AC System and Ensure Safety
Turn off your RV’s air conditioning unit and disconnect the negative battery terminal to prevent electrical shock during the repair process. Use a non-contact infrared thermometer to check if the AC is cooling properly, and listen for unusual fan noises or grinding sounds that indicate motor failure or capacitor degradation.
Step 2: Remove Rooftop AC Shroud Cover
Climb onto your RV roof and locate the fasteners holding the AC shroud in place, typically Phillips or hex-head screws around the unit’s perimeter. Carefully lift and set aside the outer cover to access the internal components, noting the position of any wiring harnesses or control board connections.
Step 3: Replace Dual Run Capacitor Unit
Locate the capacitor (a cylindrical component with two wire terminals) and take a photo of its connections before disconnecting the wires using an insulated screwdriver. Install your new Dometic or Coleman-Mach dual run capacitor by connecting the matching terminals, ensuring wires are firmly seated and not pinched or damaged.
Step 4: Remove and Test Fan Motor
Disconnect the fan motor wiring harness and remove the mounting bolts securing the motor to the AC unit’s frame. Spin the motor shaft by hand to check for grinding or resistance that suggests internal bearing failure requiring replacement.
Step 5: Install New Rooftop AC Fan Motor
Position your replacement fan motor into the mounting bracket and secure it with the original bolts, tightening firmly but not over-torquing. Reconnect the wiring harness to the motor, ensuring the connector clicks firmly into place and wires are routed away from moving parts.
Step 6: Clean Coils and Reassemble Unit
Spray AC evaporator and condenser coil cleaner foam onto the fins and let sit for five minutes, then gently rinse away debris with a soft brush or fin comb to straighten any bent fins. Apply self-leveling lap sealant around the roof gasket perimeter before reinstalling the shroud cover and fastening all screws securely.
Step 7: Test AC Cooling and Monitor Performance
Reconnect your battery, set the thermostat to a cool setting, and allow the system to run for 10-15 minutes while monitoring for proper fan operation and cool air output. Use your infrared thermometer to confirm the AC is achieving temperature differential between the intake and output air, indicating successful capacitor and motor replacement.
Recommended Parts
| Part | Link |
|---|---|
| RV AC dual run capacitor (Dometic/Coleman-Mach) | View on Amazon |
| Rooftop AC fan motor | View on Amazon |
| RV AC thermostat / control board | View on Amazon |
| AC evaporator/condenser coil cleaner foam | View on Amazon |
| Rooftop AC shroud / outer cover | View on Amazon |
| AC roof gasket & self-leveling lap sealant | View on Amazon |
| Fin comb / coil straightener tool | View on Amazon |
| Non-contact infrared thermometer | View on Amazon |