Parts that carry air
- Return-air grille
- The opening where cabin air is pulled back to the furnace or air conditioner.
- Filter
- A mesh or foam panel that catches dust before air reaches the equipment.
- Duct run
- The flexible or rigid channels under the floor or in the ceiling that distribute air.
- Roof vent
- An opening in the roof, with a fan or cover, that moves air in or out.
- Register
- The floor or ceiling opening where air enters a room.
If a smell appears only when the fan or air conditioner runs, the air system is a strong suspect. Dust, hair and moisture collect in the filter. In humid weather, the evaporator area of a rooftop air conditioner can stay wet and grow microbes. Under the floor, flexible duct can sag, collect condensation or let rodents in.
The fix depends on the cause. A dirty filter is simple. A wet drip pan needs cleaning and drainage. A duct with nesting material needs careful removal. The sections below describe how to tell which is which without taking the system apart.
RV air systems differ a lot between a small camper van and a large Class A, so use the owner's manual for the layout of your own rig. Some units move air through ceiling ducts, others through floor runs, and many small trailers have no ducting at all and rely on a single furnace vent. Knowing which type you have tells you where to look first, and it keeps you from taking apart panels that are not part of the air path. If you are not sure, a quick look with a flashlight at the registers and the return grille usually shows enough to begin.
Tracing the smell through the system
Run the fan with the equipment off
If the smell appears, it is in the cabin air or the ducts rather than the equipment.
Smell the return grille and the registers
Compare them. A stronger smell at one register points to a branch of duct.
Look at the filter
Check for dust, mold spots or a damp feel.
Inspect the rooftop shroud area
Look for a wet drip pan or mold spotting near the evaporator.
Check the outside intake
Look for nest material or debris blocking the opening.
Cleaning yourself versus bringing in help
Reasonable to try yourself
- Replacing or washing a serviceable filter
- Wiping accessible grilles
- Clearing leaves from outside intakes
- Letting the unit dry with fan-only mode
Consider an RV service professional
- Strong musty smell inside the evaporator
- Ducts that are crushed or detached
- Nest material deep in the duct
- Water leaking into the ceiling
Common questions
Do air purifiers help?
They can reduce airborne particles, but they do not remove a source such as a nest or damp insulation.
How often should filters be checked?
Check at the start of each season and after dusty or smoky trips.
General information for the Denver area, not a quote or professional advice. In an emergency, call 911.