How to Fix a Broken Window AC Drain Pan: Step-by-Step Guide

A window air conditioner works hard all summer, and a side effect of all that cooling is condensation — a steady drip of water that collects in the drain pan at the bottom of the unit. When that pan cracks, warps, or clogs, the water has nowhere to go except into your home.

A window air conditioner works hard all summer, and a side effect of all that cooling is condensation — a steady drip of water that collects in the drain pan at the bottom of the unit. When that pan cracks, warps, or clogs, the water has nowhere to go except into your home. The good news is that a leaking drain pan is a fixable DIY problem that costs very little in parts and takes only an afternoon.

Why Drain Pans Fail

Window AC drain pans are usually made from thin stamped steel or plastic. Plastic pans become brittle over years of thermal cycling, developing hairline cracks. Steel pans corrode, especially in humid climates. Both types can warp if the unit is stored improperly over winter. Clogs from algae, dust, or debris are equally common and cause overflow without any physical damage to the pan itself.

What You Will Need

• Phillips and flathead screwdrivers
• Putty knife or plastic trim tool
• Shop vacuum or wet-dry vac
• Flashlight
• Waterproof epoxy putty or clear silicone sealant (for patch repairs)
• Replacement drain pan (if patching is not viable)
• Algaecide drain pan tablets

A reliable option for patching is J-B Weld WaterWeld Epoxy Putty, which adheres to both plastic and metal and cures hard even in damp conditions.

Step 1: Unplug and Remove the AC Unit

Always unplug the unit before any disassembly. If the unit slides out of a sleeve, remove it and set it on a drop cloth on a flat surface. If it is a one-piece unit mounted directly in the window, remove it entirely by having a second person support it from outside.

Step 2: Remove the Front Grille and Access Panel

Pop off the front grille — usually held by clips or two screws. Remove the air filter. On most window units, a few more screws will free the decorative front housing, giving you a clear view of the evaporator coil and the drain pan beneath it.

Step 3: Inspect and Clean the Pan

Use a flashlight to look for cracks, holes, rust spots, and debris. Use a shop vacuum to remove standing water, dirt, and any algae growth. A clean, dry surface is essential if you are patching. Check the drain hole at the rear or side — poke a small wire or toothpick through it to confirm it is clear. Algae buildup here is a leading cause of overflow.

Step 4: Patch or Replace

Patching: If the crack is small, knead a piece of epoxy putty until it is uniform in color, press it firmly into the crack, and smooth it flat. Let it cure for the full time listed on the package — usually 1 to 4 hours. For a seamless finish, follow up with a bead of clear silicone sealant along the entire length of the crack.

Replacing: If the pan is heavily corroded, warped, or has multiple cracks, order a replacement. Search by your unit’s model number for an OEM pan, or use a universal drain pan cut to fit. Remove any retaining clips or screws holding the old pan in place, slide it out, and snap or screw in the new one.

Step 5: Add Algaecide Tablets

Before reassembling, drop one or two AC drain pan treatment tablets into the pan. These dissolve slowly over the cooling season and prevent the algae and slime buildup that clogs drain holes and accelerates pan deterioration.

Step 6: Reassemble and Test

Reinstall the front housing and filter, then plug the unit back in and run it on a cool setting for 30 minutes. Check the drain area from outside: you should see a slow, steady drip from the rear drain hole, which is normal. Check inside for any signs of moisture leaking through your repair. If the patch holds and no new leaks appear, the job is done.

Keeping the Pan Healthy Long-Term

At the start of each cooling season, pull the filter and shine a light into the pan. Clear the drain hole, add fresh algaecide tablets, and look for new cracks. This 10-minute inspection every spring can prevent a mid-summer water damage emergency. When storing the unit for winter, keep it upright so residual water drains out completely rather than sitting in the pan for months.

Related guides

• How to Fix a Window Air Conditioner — troubleshoot a window AC that’s not cooling, not draining, or running inefficiently
• How to Fix a Leaking Window AC Unit — address water leaking in or out of the unit
• AC Repair Cost — what a pro charges when DIY repair isn’t enough