Tiffin Allegro Bus – AC Capacitor & Fan Motor Service

Tiffin Allegro Bus – AC Capacitor & Fan Motor Service

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Complete repair guide for the Tiffin Allegro Bus – 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 Failure Points

Start by running your AC system and listening for unusual grinding or squealing noises from the rooftop unit, which typically indicate fan motor or capacitor failure. Use your non-contact infrared thermometer to measure the temperature differential between the air entering and exiting the AC unit—you should see a 15-20°F drop; anything less suggests a failed capacitor preventing the fan from running at full speed. Check your RV thermostat/control board display for error codes or indicator lights that point to motor or electrical component failure.

Step 2: Disconnect Power and Access Rooftop Unit

Turn off the AC breaker at your RV’s main electrical panel and verify power is cut by testing the thermostat—it should display no lights or screen activity. Climb onto your roof with your tools and locate the rooftop AC shroud/outer cover, which is typically held down by four to six fasteners around the perimeter. Remove these fasteners carefully and lift off the shroud to expose the fan motor assembly and capacitor mounted near the motor housing.

Step 3: Remove and Test the Dual Run Capacitor

Identify the cylindrical capacitor (typically rated 5-10 microfarads for Dometic or Coleman-Mach units) mounted on a bracket near the fan motor; it will have two wire terminals. Before disconnecting, take a photo of wire positions for reference, then carefully discharge the capacitor by using an insulated screwdriver to bridge the two terminals together—this prevents electrical shock from residual charge. Unscrew the mounting bracket bolts and disconnect the wire terminals, noting that the common (C) terminal usually connects to both the motor and compressor circuits.

Step 4: Install New RV AC Dual Run Capacitor

Position your new RV AC dual run capacitor in the same mounting location and secure it with the original bracket bolts, tightening firmly but not over-torquing (approximately 3-4 foot-pounds). Reconnect the wire terminals in the exact positions you documented: the common terminal to the brown wire, the fan terminal to the yellow wire, and the compressor terminal to the black wire. Double-check all connections are tight by gently tugging each terminal—loose connections will cause the AC to cycle off or fail intermittently.

Step 5: Replace Fan Motor and Inspect Coils

Unbolt the fan motor assembly (typically four mounting bolts) from the top of the AC unit and disconnect the electrical connector—note the connector orientation before removal. Install the new RV rooftop AC fan motor, ensuring the blade orientation matches the original (blades should push air downward into the unit). While the motor is accessible, spray AC evaporator/condenser coil cleaner foam across the aluminum coils, let it sit for 5 minutes, and rinse with a low-pressure spray—clogged coils reduce cooling efficiency by 30-40%.

Step 6: Seal and Reinstall Rooftop AC Shroud

Inspect the AC roof gasket for cracks, hardening, or compression loss; if the gasket is degraded, replace it with a new one to prevent water leaks into your RV interior. Apply a thin bead of AC roof gasket & self-leveling sealant around the mounting surface where the shroud contacts the roof, then carefully position the shroud and hand-tighten all fasteners in a crisscross pattern to ensure even pressure. Once all fasteners are snug (approximately 8-10 foot-pounds), apply additional sealant around the perimeter where the shroud meets the roof to create a weatherproof seal.

Step 7: Test System Performance and Verify Operation

Restore power at the main electrical panel and set your RV thermostat to cooling mode at 72°F; the fan should start immediately with a smooth, quiet operation—no grinding or squealing. Allow the system to run for 15 minutes, then use your non-contact infrared thermometer to verify the temperature differential is now 18-22°F, confirming proper airflow and motor performance. Listen for any unusual sounds, check that cool air flows consistently from all ceiling vents, and confirm the thermostat cycles on and off normally—if performance is satisfactory, your capacitor and motor replacement is complete.