--- title: "Why an RV Roof Air Conditioner Leaks in Hot Weather" description: "A ceiling drip in summer is either rain past a crushed mounting gasket or condensate overflowing a blocked pan. How to tell which, and what each one costs." focus_keyword: "why an rv roof air conditioner leaks in hot weather" canonical: https://ocrv.me/blog/august-heat-and-the-roof-air-gasket/ kind: blogPost updated: 2026-07-29 source: OCRV Center --- # August Heat and the Roof Air Gasket Nobody Checks > A summer ceiling drip has two candidate causes and they need opposite repairs. **Rain past a crushed gasket** happens in storms. **Condensate overflow** happens on the hottest, most humid afternoons. ## Why does an RV roof air conditioner leak when the weather is hot? Usually because condensate cannot leave the drain pan, or because the mounting gasket has been crushed flat and no longer seals the roof opening. At our Yorba Linda shop we separate the two by when the water appears, and Rancho Santa Margarita owners describe both as an air conditioner leak. - Water only during rain points at the mounting gasket - Water on hot humid afternoons points at the condensate path - Over tightened mounting bolts crush a gasket permanently - A gasket compressed to about half its height is correct ### Key facts | Item | Value | | --- | --- | | Roof opening served | 14 by 14 inches | | Correct gasket compression | About half of free height | | Mechanical and electrical labor | $260 per hour | | Inspection interval we suggest | Once a year, before summer | | Written estimate | $150 (Credited in full against an authorized repair) | Two owners called in the same week, both describing water at the ceiling near the air conditioner. One of them had a gasket problem and the other had a drainage problem, and the repairs share almost nothing. Guessing wrong costs a day and does not fix the leak, so this is worth ten minutes of thought before anybody climbs on a roof. The distinguishing question is when the water appears. Rain past a failed mounting gasket only shows up when it rains. Condensate overflow only shows up when the unit has been running hard in humid heat. Nobody asks that question because both leaks appear in the same place, and both feel like the same complaint. ## How a rooftop unit is actually mounted The air conditioner sits over a fourteen by fourteen inch opening in the roof, resting on a closed cell foam gasket that runs around the perimeter of its base. Inside the coach, a ceiling plate or plenum assembly bolts upward through the roof deck into the unit, and drawing those bolts down compresses the gasket between the base and the roof surface. There is no sealant in a correct installation. The gasket is the seal. That design works well and it has one vulnerability, which is that its sealing force is set by somebody with a wrench. Under tighten and the gasket does not fill the gap. Over tighten and the foam is crushed past its recovery point, at which stage it behaves like a shim rather than a gasket. Both failures leak, and the second one is far more common because tightening feels like the responsible choice. ## Why summer finishes a marginal gasket A roof surface in Orange County reaches temperatures well above the ambient air on an August afternoon, and the foam gasket under a black based appliance is in the hottest part of that. Warm closed cell foam under sustained load takes a compression set the same way any other elastomer does, only faster. So a gasket that was slightly over tightened in spring can be finished by September. The unit itself gives no indication. It cools normally, the shroud looks fine, and the only evidence is a thinner and harder gasket that nobody can see without unbolting the assembly. The first storm of the following season then produces water at the ceiling, months after the actual failure. ## The condensate path and how it blocks An air conditioner removes water from indoor air and that water has to go somewhere. On a rooftop unit it collects in a shallow pan under the evaporator and drains out through slots or weep openings in the pan onto the roof surface, where it runs off the side. That is normal and by design, and it is why you sometimes see a wet streak down one side of a coach on a humid day. Those slots block. Airborne dust, pine needles from a shaded lot, insect nests and the fine grit that lives on any roof all accumulate in the pan. Once the drain is restricted, the pan fills and overflows at its lowest inboard point, which is directly over the ceiling opening. The water then runs down inside the plenum and appears exactly where a gasket leak would appear. - Condensate is normal and drains onto the roof by design - Pan slots collect dust, needles and insect nests over a season - A restricted pan overflows inboard, straight into the ceiling opening - A wet streak on the outside of the coach is drainage working correctly ## Telling them apart without removing anything Ask when. Water during or shortly after rain, with the air conditioner off, is the gasket. Water on a hot humid afternoon with the unit running for hours, and no rain anywhere, is the condensate path. Water in both conditions means you have both problems, which happens more often than it should because the same neglect produces both. Then look at the ceiling plate. Gasket water tends to arrive at one corner of the plate and stain outward from it, following the perimeter where the seal failed. Condensate overflow arrives more centrally, through the plenum and the filter area, and often smells faintly of the evaporator rather than of nothing at all. Neither observation is definitive alone and together they are usually enough. > **note:** Do not run a bead of sealant around a rooftop air conditioner base. It will not fix a crushed gasket, it makes removal considerably longer, and it can block the drainage path the pan depends on. ## What each repair actually involves A blocked drain is a cleaning job. The shroud comes off, the pan is cleared with a soft brush and a vacuum, the slots are opened with a plastic pick, the evaporator fins are cleaned, and the shroud goes back on with fresh fastener grommets. Under an hour on most units, and the shroud fasteners are worth replacing while it is open because they are usually the original plastic and brittle by then. A gasket replacement is a bigger operation. Interior plate down, mounting bolts out, unit lifted clear of the opening, old gasket removed from the base, roof surface cleaned, new gasket set, unit lowered and rebolted to the correct compression rather than to feel. Lifting a rooftop unit is a two person job by weight alone, which is most of the reason it belongs in a bay. ## The annual check that prevents both Once a year, before summer, take the shroud off and look. You are checking three things and it takes fifteen minutes: whether the drain slots are clear, whether the evaporator fins are clogged with dust, and whether the gasket is visibly squeezed out beyond the base edge in an uneven way. Photograph the gasket line while you are up there, because year to year comparison is the only way to see it thinning. While the shroud is off, check the shroud fasteners themselves. Ultraviolet exposure makes those plastic screws and grommets brittle, and a shroud that departs on the freeway takes the fan cover with it and leaves the evaporator open to the weather. That is a cheap part and an annoying failure, and it happens for no reason other than nobody looked. ## Questions and answers ### How do I know whether my RV air conditioner leak is rain or condensate? Note when the water appears. Rain only, with the unit switched off, indicates the mounting gasket. Hot humid afternoons with the unit running for hours and no rain indicates a blocked condensate pan. Water in both conditions means both problems exist, which is common because one kind of neglect causes each. ### Can you over tighten the bolts on a rooftop air conditioner? Easily, and it is the more common error. The mounting bolts set the sealing force on a foam gasket, and crushing that foam past its recovery point turns it into a shim rather than a seal. Correct compression is roughly half the gasket's free height, which feels loose to anyone expecting a hard stop. ### Is water running down the side of my RV from the air conditioner normal? Yes, that is the drainage system working. Condensate collects in a shallow pan and exits through slots onto the roof, then runs off the side. A wet streak on a humid day is expected. The problem is the opposite case, where nothing drains outside and water appears at the ceiling instead. ### Should sealant be applied around the base of a rooftop unit? No. A correct installation seals on the gasket alone. Sealant will not restore a crushed gasket, it can obstruct the pan drainage path, and it makes any future removal considerably longer because the bead has to be cut and cleaned off the membrane before the unit can lift. ### Why replace the shroud fasteners during an air conditioner service? Because ultraviolet exposure makes those plastic screws and grommets brittle, and a shroud that leaves at freeway speed exposes the evaporator to weather and debris. They cost very little, they are already accessible whenever the shroud is off, and replacing them removes an entirely avoidable failure. --- Source: [OCRV Center](https://ocrv.me/blog/august-heat-and-the-roof-air-gasket/). Last verified 2026-07-29.