RV Roof Leak Around an AC Unit

Water dripping from a roof air conditioner is usually the gasket, not the roof. The A/C isn’t sealed with lap sealant like a vent or skylight. It sits on a thick foam gasket over a standard 14-by-14-inch opening, clamped down by bolts from inside the ceiling. That’s why a bead of caulk around the shroud, a common DIY fix, doesn’t work and makes the leak harder to find.

Is it a roof leak or A/C condensation?

Water at the ceiling grille has two very different sources, and timing tells them apart.

• Drips during or after rain, with the A/C off: the gasket, or the roof membrane near the opening. A real leak
• Drips on hot, humid days while the A/C is running hard: almost certainly condensate. The unit is making water faster than its drain pan sheds it. Often the pan’s drain holes are clogged or the RV is parked off-level
• Both: it happens. Check the condensate side first, because it’s the quicker check

Condensate problems are maintenance, not roof repair. Clear the pan, check your level, and the “leak” often vanishes.

Why does an RV A/C gasket leak?

The gasket is foam doing a compression job for years, through thousands of kilometres of road vibration and every freeze-thaw swing Ontario offers. Eventually it squashes flat, loses its spring, and stops sealing. Installation mistakes speed that up from both directions. Overtightened bolts crush it flat on day one, and loose bolts let the unit rock and work free. If your A/C was ever removed and reinstalled, the gasket and its bolts are the first suspects.

How do you fix a leaking RV A/C gasket?

Start from inside. With the ceiling grille off, the mounting bolts are right there. Sometimes the fix is bringing them back to the tightness in the A/C maker’s install guide: snug and even, not cranked down. If the gasket has gone flat and hard, the unit comes off, the flange gets cleaned, and a new gasket goes on. While the unit is up, we check the membrane under it too. Now and then the gasket takes the blame for a split in the roof nobody could see.

Why shouldn’t you caulk around an RV A/C?

Sealing the shroud to the roof traps water inside it, and the shroud is vented on purpose. It also hides where water is really getting in, and it smears product onto membrane that the proper repair has to clean off. If there’s water at your ceiling grille, put the caulking gun down. This is a diagnosis job first, and a quick one with a moisture meter and a reason to look.