Different brands fail in different ways — and once you’ve serviced enough of them, you start building a mental map of which rig is going to have which problem. That brand-specific pattern recognition is what separates a tech who’s been doing this for years from someone who’s just good with tools. With Grand Design Reflections, the air conditioning system is one of those things I’ve learned to watch closely — a failing run capacitor or a worn-out fan motor will take your cooling unit down fast, and in the middle of summer at a crowded campground, that’s not a small problem. The tricky part is that a weak capacitor often mimics other issues — the unit might try to start, grunt, trip the breaker, or just blow warm air — so without knowing what you’re actually looking for, it’s easy to chase the wrong fix. This guide is built from real on-site service calls on these exact units, so whether you’re troubleshooting from your campsite or prepping before you call a tech, you’ll know exactly what’s going on and what it’s going to take to get your AC back online.
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 & Ensure Safety
Start by identifying symptoms such as weak airflow, unusual humming sounds, or complete AC failure to determine if capacitor or motor replacement is needed. Before beginning work, disconnect your RV from shore power, switch off the thermostat, and allow the unit to sit for 15 minutes to discharge any residual electrical current from the capacitor.
Step 2: Remove Rooftop AC Shroud Carefully
Climb onto your RV roof and locate the fasteners securing the outer AC shroud or cover, typically held by four to six bolts or screws around the perimeter. Carefully lift and set aside the shroud, noting the position of any wiring harnesses connected to the thermostat control board for easier reassembly.
Step 3: Access & Replace Dual Run Capacitor
Locate the cylindrical capacitor mounted inside the AC unit, typically labeled with microfarad (µF) ratings matching your specifications. Using an insulated screwdriver, discharge the capacitor by touching the blade across the terminals, then disconnect the wire terminals and remove the mounting bracket before installing your new dual run capacitor in reverse order.
Step 4: Inspect & Service Fan Motor Assembly
Examine the fan motor for corrosion, loose connections, or blade damage that may impede performance. If the motor shows signs of wear but still functions, clean the motor housing and fan blades with the AC coil cleaner foam to remove dust and debris that reduces efficiency.
Step 5: Replace Fan Motor If Necessary
If your motor is non-responsive or severely damaged, disconnect the electrical harness and remove the mounting bolts securing the motor to the housing. Install the new motor, ensuring proper alignment with the fan blade coupling, then reconnect the electrical terminals according to the wiring diagram on your control board.
Step 6: Clean Coils & Reseal Roof Gasket
Apply AC evaporator/condenser coil cleaner foam across the cooling coils and use a fin comb to straighten any bent fins that restrict airflow. Once coils are dry, inspect your roof gasket around the AC unit’s base and apply self-leveling lap sealant to any cracks or gaps to prevent water intrusion.
Step 7: Test System Performance & Airflow
Reassemble the shroud, reconnect shore power, and set your thermostat to cooling mode at 65°F to activate the system. Use your non-contact infrared thermometer to verify that cold air is flowing from vents (typically 40–50°F) and listen for the fan motor to run smoothly without grinding or rattling sounds.
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 |