ServiceNomad RV · Knowledge
RV AC Blowing Warm Air
Turning on your RV's air conditioner on a sweltering day only to feel lukewarm air is a common and frustrating experience. Unlike residential systems, RV AC units are sealed systems that sit on the roof, exposed to extreme heat and vibration. When they blow warm, the issue is typically related to airflow restrictions, compressor failure to launch, or dirty heat exchange coils. Before calling a mobile technician, understanding the basic operation of your unit can save you a service call. The system relies on moving heat from inside to outside; if any part of that exchange is blocked, cooling stops.
Airflow Restrictions and Filters
The number one cause of an RV AC freezing up or blowing warm is simply a lack of airflow. The evaporator coil (inside the RV) needs warm air moving across it to keep from freezing. If your return air filters are clogged with dust or pet hair, the airflow drops, the coil gets too cold, ice forms, and eventually, the air passage is blocked completely. Check your ceiling assembly. Remove the foam filters and wash them. Also, use a flashlight to look up into the ducting. Sometimes the foil tape separating the 'return' (warm air in) and 'supply' (cold air out) comes loose. If these two mix, the AC just recycles its own cold air short-cycling the thermostat or freezing the coil.
Dirty Condenser Coils (Roof)
Up on the roof, under the plastic shroud, lies the condenser coil. Its job is to release the heat pulled from your RV. If this coil is matted with cottonwood, leaves, or dirt, it cannot shed heat. The compressor will overheat and shut down on its thermal safety switch, leaving only the fan blowing warm air. Safety Note: You can clean this yourself with a hose and gentle pressure, but be careful not to bend the delicate aluminum fins. If the fins are bent flat, airflow is blocked, and the unit will overheat.
Compressor Start Components
If you hear the fan running but not the low rumble of the compressor, your compressor isn't starting. This is often due to a failed 'start capacitor' or 'hard start kit'. These components store energy to give the compressor the jolt it needs to start. Capacitors are common failure points in RVs due to heat and voltage fluctuations at campgrounds. A technician can easily test and replace these. If the capacitor is good but the compressor won't start (and draws huge amps), the compressor itself may be seized.
💡 Prevention Tips
- Clean return air filters every 2 weeks of continuous use.
- Visually inspect roof condenser coils annually.
- Install a SoftStart device to reduce strain on the compressor.
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