How RV AC Cooling Systems Work

Your RV air conditioner uses refrigerant (typically R410A in modern units) that circulates through a closed loop, changing from liquid to gas and back again. The compressor, located in the rooftop unit, compresses refrigerant gas, raising its temperature and pressure. This hot, high-pressure gas flows to the condenser coils (the ones exposed to outside air on top of your RV), where fans blow air across the coils to remove heat. As heat dissipates, the refrigerant condenses back into a liquid.

RV air conditioners face challenges home units don't. They must handle extreme vibration during travel, temperature swings from freezing winters to desert summers, and exposure to UV radiation that degrades plastic and rubber components. Most critically, RV AC units sit on your roof fully exposed to weather, unlike protected home units. This exposure means seals, gaskets, and mounting hardware deteriorate faster. RV AC units are also more compact and operate at higher ambient temperatures. Residential AC units typically have outdoor condensers at ground level where temperatures are cooler. RV units have their condensers on a black roof, sometimes in 140-degree heat. This means RV compressors work harder and run hotter, stressing components. The compact design also means less space for efficient heat exchange, which is why RV AC units have lower BTU capacity relative to their power consumption compared to home units. A single RV rooftop unit typically provides 13,500 or 15,000 BTUs - enough for a small to mid-size RV, but larger coaches often need two or three units.

The compressor is the heart of the system, pumping refrigerant through the loop. Most RV AC compressors last 5-10 years with proper maintenance but can fail earlier from excessive heat or liquid refrigerant entering the compressor (called 'slugging'). The condenser fan pulls hot outside air across the condenser coils to dissipate heat. If this fan fails, the compressor overheats and shuts down on its thermal limit switch. The evaporator fan (inside) blows cabin air across the cold evaporator coils, distributing cool air through your RV. If this fan quits, you'll feel little or no airflow even though the unit is running. The capacitor (a cylindrical component visible inside the unit) provides the electrical boost needed to start the compressor and fans. Capacitors are the most common failure point in RV AC systems - they weaken over time and eventually can't provide enough starting power. When a capacitor fails, you might hear clicking or humming but the compressor won't start. The thermostat or control board tells the AC when to run. Modern digital controls can fail from power surges, while mechanical thermostats can stick or lose calibration. Refrigerant itself doesn't wear out, but it can leak through deteriorated seals, o-rings, or vibration-cracked lines.

A properly functioning RV AC should cycle on and off based on thermostat settings. You'll hear the compressor kick on with a slight hum or rumble, fans start blowing, and cool air emerges from vents within a minute. The unit should cool your RV to the setpoint temperature, then cycle off, then restart when temperature rises. Some cycling is normal and healthy - it prevents the unit from freezing up and gives components rest periods. Abnormal sounds include grinding (failing bearings), loud clicking that doesn't result in starting (bad capacitor or relay), or continuous running without cooling (low refrigerant, failed compressor, or blocked airflow). Freezing evaporator coils indicate airflow problems or refrigerant issues - ice blocks airflow and prevents cooling. Water dripping inside the RV means the drain pan is clogged or the unit is tilted, preventing proper drainage. Electrical smells or smoke mean immediate shutdown and professional help. Weak airflow might seem minor but indicates dirty coils or failing fans that, if ignored, lead to compressor damage from overheating.

RV AC systems are sealed refrigeration systems. Homeowners cannot legally purchase refrigerant or the equipment to properly evacuate and recharge systems - this requires EPA certification. Attempting to 'top off' refrigerant without proper training risks overcharging (which damages compressors), environmental harm, and personal injury from high-pressure refrigerant. Professional technicians use manifold gauges, recovery machines, vacuum pumps, and electronic scales to properly service these systems. Diagnosing AC problems also requires understanding electrical circuits, refrigeration theory, and how these interact. A capacitor might test fine when cold but fail when heated to operating temperature - catching this requires experience. Compressors can fail mechanically (seized bearings) or electrically (shorted windings), and distinguishing between them requires specific testing procedures. Control board issues can mimic mechanical problems, leading to unnecessary part replacement without proper diagnosis. Professional technicians can accurately identify the failing component, source the correct replacement parts, and restore your system efficiently.