Call a tech about a dripping window unit, and nine times out of ten the fix is in how it sits in the opening. It’s rarely the compressor or the coil. So before you pay for a repair, go through these four.
Tilt
This is the one that causes leaks. A window AC pulls water out of the air as it cools, and the only way that water leaves is out the back. That means the whole unit has to lean slightly toward the outdoors. We’re talking about a quarter inch of drop front to back, roughly 2 to 4 degrees. Set a small level on top of the cabinet and aim for about a third of a bubble toward the outside.
Level isn’t good enough. Level means the water sits in the pan until it spills over the front. Steeper isn’t better either, since a unit pitched too far makes the fan blades hum and drags cooling down.
Older sills lie. Half an inch out of true is common, so put the level on the sill before the unit goes anywhere and shim the low side. Side to side, you do want it dead level, or the water slides to one end of the pan.
Don’t touch the drain. The pan is designed to sit about half full, so never drill it, and keep caulk off the drain ports. If a storm window frame sits right behind the cabinet and blocks them, lift the unit above it or pull the frame.
Run the unit for 10 to 15 minutes and walk outside. A steady drip means you did it right. Meanwhile, having water indoors means it needs a little more lean. If the lean is right and the window AC still drips inside, look at the filter. If it’s clogged, it freezes the coil. The meltwater floods the drain.
Weight
Forty pounds or more, and most of it hangs outside the glass. Keep both hands on it until it’s seated. After that, the sash and sill can’t carry it alone for long. They flex, the unit creeps, and eventually it rattles. A window AC that’s hung off its sash for a whole season is the one you hear from the other room.
Get a support bracket. It moves the load off the window and protects the wall beneath, and above the second floor I treat it as required. Fasten the bracket loosely first, then turn its leveling bolt until you have that quarter inch of lean. Tighten everything down.
A wood sill needs pilot holes before any screw goes in, or it can split. Vinyl windows are fussier. Put one screw through the locking bracket into the side jamb and stop there.
Panels and Sash
Seat the bottom rail against the back edge of the sill and center the cabinet. Then bring the window down behind the top rail, and I mean firmly. If the sash only brushes that rail, you’ll hear it buzz all summer.
The accordion panels pull out to the sash tracks. Screw through their holes, left panel on the left and right on the right, because they aren’t interchangeable. The frame locks go under the panels and into the sill.
Why all the fuss about screws? Most of the rattles I’d chase turn out to be a loose panel or a lock that never got fastened. A corner that still hums after that usually quiets down with a thin shim slid underneath.
Gaps
Warm air comes through gaps. So do rain and insects. Every one of them gives back some of the cooling you paid for.
Peel the backing off the foam seal and press it onto the underside of the sash. Cut the thick foam strip to the width of the window and push it into the gap between the panes at the top. Trim the insulating panels and lay one over each accordion. Whatever is still open to the outside gets caulk or weatherstrip, as long as it stays off the drain holes.
Then stand outside and look at the front of the unit. Light around the edges means air is leaking, and a sealed install shows none.