Evaporative cooler leak water damage in Casa Grande, AZ

Why these coolers leak in the first place

An evaporative cooler pulls outside air through wet pads. A small pump circulates water from a pan in the bottom of the unit up to the pads, and a float valve tops the pan back up as water evaporates. So the unit holds several gallons of standing water the whole time you run it, spring through the end of the hot season. On most older Casa Grande homes it sits on the roof directly over living space, or hangs on an exterior wall. Water only has to escape the pan to end up inside the house.

The common failure points:

• A stuck float valve. It should shut the fill off at a set level. When scale builds on it or the float arm bends, it keeps feeding water and the pan overflows.
• A rusted pan. Sheet metal pans sit in water for months, then pit and rust through at a seam or corner, and the leak drips onto the roof.
• A cracked supply line. The small copper or plastic line bakes in Casa Grande sun all summer. Fittings loosen, and plastic goes brittle and splits.
• A clogged overflow. The overflow tube dumps excess water safely. Dust, mineral crust, and algae plug it, so the pan spills over the side instead.
• A disconnected bleed-off line. The bleed-off drains a little water constantly to keep minerals from concentrating. If it comes loose or was never routed to a drain, it pours onto the roof or against a wall all season.

Warning signs to look for

The unit is out of sight, so the house tells you before the cooler does. Watch for:

• A brown or yellow ring on the ceiling directly under or near the unit
• Drywall that feels soft, sags, or has bubbling or peeling paint
• A musty or earthy smell in one room that does not clear
• Rust streaks or a chalky white mineral trail down an exterior wall under a wall-mount cooler
• A water bill that jumped with no change in how you use water
• Nail heads or seams showing through the ceiling texture, or a hairline crack that keeps growing
• The pads staying soggy long after the cooler shuts off, which points to a float that will not close

Why the damage is usually found late

Nobody climbs on the roof in July. The leak starts small, and the water travels before it shows up. It follows the roof deck, runs along a rafter, or drops down the duct chase and soaks insulation on the way, and insulation absorbs a lot before anything drips. By the time a stain appears, the sheathing above it and the top plate of the wall have often been wet for weeks. See our ceiling water damage page for what those stains mean.

Cooler season also overlaps with monsoon season, so a stain that shows up in August gets blamed on the storm while the real source keeps running.

How the cleanup and drying works

First the water stops. Shut the valve on the supply line to the cooler and cut power to the unit, not just the switch inside. Then the crew maps how far the water went. Moisture meters and a thermal camera show the wet footprint on the ceiling, and it is usually much bigger than the visible stain. From there:

• Extraction. Any standing water in the pan, on the roof deck, or on the floor below comes out first.
• Opening the ceiling. Saturated drywall does not dry in place, and wet blown-in insulation holds water like a sponge. Both usually come out so the cavity can dry.
• Drying the structure. Air movers and commercial dehumidifiers pull moisture out of the framing, the top plates, and the sheathing. Readings get checked daily until the wood and drywall are back to normal levels.
• Checking the walls. Water that runs down a wall cavity soaks the bottom plate and the base of the drywall. That gets checked even when the wall looks fine from the room.
• Documenting it. Source, category of water, affected area, and daily moisture logs, in the format an adjuster expects.

Water from a cooler pan is not clean water. It sits in an open pan collecting dust and whatever blew in off the roof, and it circulates through pads that grow algae. Crews treat it as Category 2, so affected materials get cleaned and treated, not just dried. Our water damage restoration page walks through the full drying process.

The mold risk from a slow leak

A slow cooler leak is close to the worst case for mold. The moisture is steady rather than a one-time soak, it sits in a dark enclosed cavity, and it runs for weeks before anyone catches it. Paper-faced drywall, insulation, and roof sheathing all feed mold once they stay damp, and the dry Casa Grande air outside does nothing for a sealed ceiling cavity.

If a leak has run long enough to stain a ceiling, assume growth is possible and have it looked at. Watch for a musty smell that strengthens when the cooler runs, and dark speckling on the back of removed drywall. Our mold remediation page covers containment and removal.

Seasonal checks that prevent most of this

Two short inspections a year catch nearly every one of these failures.

Spring start-up, before you turn the water on:

• Look at the pan for rust, pinholes, and soft spots at the seams and corners
• Work the float arm by hand and make sure the valve shuts completely
• Flush the overflow tube and the bleed-off line, and confirm the bleed-off actually goes to a drain and not onto the roof
• Check the supply line and every fitting for cracks, brittleness, and drips
• Replace scaled or crumbling pads and clear mineral crust out of the pan
• Run it for ten minutes with the water on and watch for anything wet outside the unit

Fall shut-down, when the season ends:

• Shut the water off at the valve on the supply line, not just at the switch
• Drain the pan completely and dry it out
• Drain the supply line so nothing sits in it over winter
• Cover the unit and check that the cover keeps rain out of the housing

While you are up there, check the roof around the cooler stand. Discolored roofing, a soft spot underfoot, or loose flashing means water has already been getting in.