What causes my RV to smell like my holding tanks when the A/C is running?

Your RV’s air conditioner unit works by drawing in the hot air from inside your RV, expelling heat outside of the RV, and then pushing the cool air back into your RV through the air vents. RV air conditioners are located on the roof of your RV, obviously, which also happens to be where your RV’s holding tank vent pipes are located.

Our guess is that your air conditioner is pulling smelly air up through the vent pipe, into the unit, and out into your RV’s interior. This wouldn’t normally be an issue when the RV is outside in (somewhat) windy (to some degree) weather, but if the RV is being stored inside or in a wind-protected area, the unit is most certainly siphoning off sewage gases.

If your RV’s sewage system vent pipe doesn’t have a cap on it, consider adding one to help minimize the siphoning situation. The Camco Cyclone is an excellent wind-powered pipe cap that will draw tank odors away from your RV. It also is a bit better “contained” than just a standard cap and may deter some siphoning of sewage gases in low-wind situations.