Why Is My Air Conditioner Leaking Water Inside?

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What's Actually Causing the Leak

Central air conditioners produce a steady stream of condensation as warm, humid air passes over the cold evaporator coil. Normally that water drains through a condensate line to the outside or into a floor drain. When you see water pooling near your furnace or air handler, or dripping from a ceiling if the unit is in an attic, something is interrupting that drainage path.

• Clogged condensate drain line - algae, dust, and debris build up inside the drain pipe over time and block the flow, backing water up into the drain pan and overflowing it.
• Dirty or clogged air filter - restricted airflow across the coil causes it to get too cold and freeze; when the system cycles off or you notice it and turn it off, the ice melts all at once and overwhelms the drain pan.
• Cracked or rusted drain pan - older metal pans corrode over time, especially in humid crawlspaces or basements, and start leaking directly through the pan itself.
• Disconnected or poorly sloped drain line - if the line was installed without enough slope, or a fitting has come loose, water won't drain properly even if the line isn't clogged.
• Low refrigerant - a system low on refrigerant can cause the coil to run too cold and ice over, with the same freeze-then-melt leak pattern as a dirty filter.

What to Check Before Calling for Service

A few things you can safely check yourself first. Turn the system off at the thermostat so any ice on the coil has a chance to melt and you're not adding more water to the problem.

• Check and replace the air filter if it's visibly dirty - this is the single most common cause and the easiest to rule out.
• Look at the condensate drain line where it exits the house (usually a white PVC pipe near the outdoor unit or foundation) and see if water is flowing out when the system runs.
• Check the drain pan under the indoor unit for cracks, rust holes, or standing water.
• If you have a wet/dry shop vac, you can sometimes clear a clog at the drain line's outdoor termination point yourself.

When to Call a Professional

If clearing the filter and checking the drain line doesn't stop the leak, or if you see ice on the refrigerant lines or coil, it's time to have a technician take a look. A stuck clog further inside the line, a cracked drain pan, or low refrigerant all require tools and diagnostic equipment homeowners don't typically have on hand. Refrigerant issues in particular should never be handled as a DIY job - refrigerant is a controlled substance and low levels usually mean there's a leak somewhere in the system that needs to be found and sealed properly. We offer a diagnostic visit with a free written quote so you know exactly what's wrong and what it'll cost to fix before any work starts. If you're in Metro Vancouver and dealing with an active leak, call us at (604) 359-1081.

Frequently asked questions

Reviewed by the CANRO Heating & Cooling service team — July 07, 2026. Technical Safety BC gas licence LGA0043870 · boiler licence LBP0046450 · Red Seal certified · WorkSafeBC and liability insured · 4.9★ from 85+ Google reviews · serving Metro Vancouver since 1999 · (604) 359-1081.