The calls I get on holiday weekends are always the same energy: a family parked at a campground, kids in the background, and a very stressed adult trying to describe a sound or a symptom over the phone. I always ask the same first question: when did you first notice something was off? The answer is almost never “today.” With AC systems, it usually started days earlier — a unit that took longer than usual to cool down, a fan that sounded like it was working too hard, or a compressor that kicked on and then just… gave up. Nine times out of ten, when I pull the access panel on a rooftop AC unit, I find a swollen or failed run capacitor and a fan motor that’s been straining against it, and by the time someone calls me, the whole system has finally said enough. This guide walks you through diagnosing and replacing both the capacitor and fan motor on your RV’s AC unit — the right way, in the right order — so you’re not waiting on a technician to show up while your rig turns into an oven.
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 Issues and Safety First
Before beginning any work, turn off your RV’s electrical system at the main breaker and disconnect shore power to ensure your safety while working with electrical components. Use your non-contact infrared thermometer to measure current cooling output and listen for unusual noises from the rooftop unit, which will help you identify whether the capacitor or fan motor is failing.
Step 2: Remove Shroud and Access Components
Climb onto your RV roof safely using a ladder and secure footing, then locate the four to six bolts holding the AC shroud in place. Carefully unbolt and lift off the outer cover to expose the dual run capacitor, fan motor, and internal coils underneath.
Step 3: Replace Dual Run Capacitor Unit
Before disconnecting anything, take a photo of the wire connections to the old capacitor for reference during reinstallation. Carefully discharge any remaining electrical charge by using an insulated screwdriver to bridge the capacitor terminals, then unbolt the old capacitor and disconnect its wires, sliding the new Dometic or Coleman-Mach capacitor into place and reconnecting the wires in their original configuration.
Step 4: Clean Evaporator and Condenser Coils
Spray your AC coil cleaner foam generously over both the evaporator coils (inside the unit) and condenser coils, allowing the foam to sit for the manufacturer’s recommended time to break down dirt and debris buildup. Use your fin comb tool to straighten any bent aluminum fins on the coils, working gently to improve airflow and cooling efficiency.
Step 5: Install New Fan Motor Assembly
Unbolt the old fan motor by removing the mounting brackets and carefully disconnect its wiring harness, taking another photo for reference before removal. Position your new rooftop AC fan motor into the mounting location, reconnect the wiring harness according to your reference photo, and securely bolt the motor down to ensure it won’t vibrate during operation.
Step 6: Reseal Shroud and Inspect Gasket
Before reinstalling the shroud, inspect your AC roof gasket for cracks, hardening, or deterioration and replace it if necessary to prevent roof leaks. Apply self-leveling lap sealant around the gasket area and along the shroud seams, then carefully lower the shroud back into position and reinstall all bolts in a star pattern to ensure even pressure.
Step 7: Test System and Monitor Performance
Restore power to your RV and turn on the AC system, observing the fan motor for smooth operation and listening for any unusual grinding or squealing sounds that would indicate installation problems. Use your infrared thermometer to confirm that cool air is being produced and measure the temperature difference between the intake and output vents, with a properly functioning system typically showing a 15-20 degree temperature drop.
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 |