Tiffin Open Road Allegro – AC Capacitor & Fan Motor Service

Tiffin Open Road Allegro – AC Capacitor & Fan Motor Service

by

Complete repair guide for the Tiffin Open Road Allegro – AC Capacitor & Fan Motor Service. Follow these steps to diagnose and fix the issue yourself.

Parts & Tools You’ll Need

Step 1: Diagnose AC Performance & Safety Checks

Start by testing your AC system while parked in a safe location with the engine off and all slide-outs retracted. Turn on the air conditioning and listen for unusual grinding or squealing noises from the rooftop unit, then use your non-contact infrared thermometer to measure the air temperature coming from interior vents—it should reach 20-30°F below the ambient outdoor temperature within 10 minutes. If the fan motor runs but produces weak airflow, or if you hear a humming sound without fan rotation, you likely have a failed capacitor; if there’s no fan response at all, suspect the motor itself or a tripped breaker on your RV’s main panel.

Step 2: Power Down & Access Rooftop Unit

Flip the AC circuit breaker to OFF on your RV’s electrical panel to eliminate shock hazard, then wait 5 minutes to allow residual capacitor charge to dissipate. Climb onto your roof using a stable ladder and locate the rooftop AC shroud—typically a rectangular plastic cover measuring roughly 24 inches by 30 inches with four corner bolts and a central duct connection. Remove the rooftop AC shroud by unscrewing the four corner fasteners and carefully lifting the cover straight up to avoid damaging the aluminum trim and AC roof gasket underneath.

Step 3: Remove & Test Dual Run Capacitor

Locate the dual run capacitor inside the unit—it’s a cylindrical or oval component typically mounted on a bracket near the compressor, rated between 30-50 microfarads (µF) depending on your Dometic or Coleman-Mach model. Photograph the wire terminal positions (usually labeled C, H, and F) before disconnecting them, then use an insulated screwdriver or needle-nose pliers to gently pull the push-on terminals free. Take the capacitor to an HVAC supplier to have it tested with a capacitor meter; a failed unit will read zero or an incorrect µF value, confirming replacement is needed.

Step 4: Install Replacement Capacitor & Wiring

Position your new RV AC dual run capacitor in the same orientation as the original, ensuring the bracket mounting holes align perfectly. Reconnect the three wire terminals to their corresponding posts (C to compressor, H to heat, F to fan)—push firmly until you hear a distinct click, then give each terminal a gentle tug to confirm a secure connection. Verify terminal polarity matches your photographic reference; reversed connections will prevent fan operation and can damage the control board.

Step 5: Service Fan Motor & Coils

Inspect the rooftop AC fan motor—a small electric motor typically located near the intake shroud with a 4-6 inch diameter aluminum fan blade. If the motor shaft rotates freely by hand and shows no visible corrosion or bearing damage, clean the AC evaporator and condenser coils with the foam coil cleaner, spraying from the inside outward to flush debris toward the roof drains. Use the fin comb / coil straightener tool to carefully straighten any bent aluminum fins on the coil pack, working in one direction only to avoid creating new damage.

Step 6: Reinstall Shroud & Verify Gasket Seal

Before replacing the rooftop AC shroud, inspect the AC roof gasket for cracks, hardening, or separation—if it’s degraded, apply fresh self-leveling sealant along the entire perimeter where the gasket contacts the roof. Lower the shroud straight down over the unit, centering it so the gasket seats evenly, then hand-thread all four corner bolts and tighten them in an X pattern (opposite corners alternately) to 12-15 foot-pounds using a torque wrench. Apply additional self-leveling sealant around all four bolt heads and allow 24 hours for cure before testing the system.

Step 7: Power Up & Performance Verification

Switch the AC circuit breaker back ON and allow the system to stabilize for 3-5 minutes before engaging the air conditioning at maximum cool setting. Measure interior vent air temperature again with the non-contact infrared thermometer—you should achieve at least a 20°F temperature differential between indoor and outdoor air within 10 minutes, and the fan should run smoothly without vibration or noise. Listen for proper compressor cycling (running 15-20 minutes, then shutting down for 10-15 minutes), which indicates the capacitor and motor are functioning correctly; if the system still underperforms, the compressor itself may require service.