Keystone Alpine – AC Capacitor & Fan Motor Service

by

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

Parts & Tools You’ll Need

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

Before starting any work, you’ll need to identify whether your cooling problems stem from a failed capacitor or fan motor by listening for humming sounds without the fan spinning, or complete AC failure. Turn off power at your RV’s breaker panel and disconnect the negative battery terminal to ensure you’re working safely, then wait several minutes for residual electrical charge to dissipate from the capacitor.

Step 2: Remove AC Shroud & Access Components

You’ll need to carefully unscrew and lift off the rooftop AC shroud or outer cover, taking photos of the wire connections before disconnecting them for reference during reassembly. Set the shroud aside in a safe location where it won’t get damaged, as you’ll be reinstalling it once your service work is complete.

Step 3: Replace Dual Run Capacitor Unit

You should locate the cylindrical capacitor (typically labeled with microfarad ratings like 40/5 µF) and use a capacitor discharge tool or insulated screwdriver to safely drain any remaining charge before disconnecting the wire terminals. Note the wire positions, disconnect them carefully, unscrew the mounting bracket, and install your new Dometic or Coleman-Mach capacitor in reverse order, ensuring all connections are tight and secure.

Step 4: Service Fan Motor Assembly

You’ll disconnect the fan motor’s electrical connectors and unbolt it from its mounting brackets, then inspect the motor shaft for debris or corrosion that might impede rotation. Clean the motor exterior with compressed air and check that the new replacement motor matches your original specifications before installing it with all fasteners torqued securely.

Step 5: Clean Evaporator & Condenser Coils

You can now spray the AC coil cleaner foam directly onto both the evaporator and condenser coils, allowing it to sit for the manufacturer’s recommended time to break down dirt and algae buildup. After the foam has worked, use a fin comb or coil straightener tool to carefully straighten any bent fins, being gentle to avoid damaging the delicate aluminum fins that affect cooling efficiency.

Step 6: Reinstall Shroud & Seal Gasket

You’ll position your rooftop AC shroud back into place and reconnect all wire terminals to their original positions using your reference photos, then secure all mounting screws and bolts. Apply fresh RV AC roof gasket material and self-leveling lap sealant around the shroud perimeter and any penetration points to prevent water leaks and maintain your roof’s integrity.

Step 7: Test AC System & Monitor Performance

You should restore power at the breaker and reconnect your battery, then turn on the AC system to verify the fan motor spins smoothly and the compressor engages without unusual noises. Use your non-contact infrared thermometer to measure the temperature difference between the AC output vent and return air—you should see at least a 15-20 degree temperature drop indicating proper cooling performance.

Recommended Parts

PartLink
RV AC dual run capacitor (Dometic/Coleman-Mach)View on Amazon
Rooftop AC fan motorView on Amazon
RV AC thermostat / control boardView on Amazon
AC evaporator/condenser coil cleaner foamView on Amazon
Rooftop AC shroud / outer coverView on Amazon
AC roof gasket & self-leveling lap sealantView on Amazon
Fin comb / coil straightener toolView on Amazon
Non-contact infrared thermometerView on Amazon