How to Clean a Clogged AC Drain Line

What you need

• Wet/dry shop vacuum
• Distilled white vinegar
• Flashlight
• Small bucket or towel
• Duct tape or a rag for sealing the vacuum hose against the pipe
• Funnel (optional, for the access port)

Step-by-step

1. 1

   Turn off the AC system

   Switch the thermostat to OFF, then turn off the breaker or disconnect that powers the indoor air handler. This stops condensation from being produced while you work and protects you from contact with energized components near water.

2. 2

   Locate the drain line and access port

   Find the PVC pipe that exits the side of your house near the outdoor condenser or foundation—that is the drain line termination. Indoors, look for a T-shaped fitting with a removable cap on the PVC pipe near the indoor air handler or furnace. That cap is the access port for flushing.

3. 3

   Vacuum the clog from the outdoor end

   Place the wet/dry vacuum hose over the outdoor drain line exit. Seal the gap with duct tape or a rag so suction is not lost. Run the vacuum for 2–3 minutes to pull out algae, dirt, and debris. You will often see a dark clump of sludge enter the vacuum.

4. 4

   Flush the line from the indoor access port

   Remove the cap from the indoor access port. Pour a cup of distilled white vinegar into the opening to break down remaining biofilm. Wait 30 minutes, then flush with a gallon of warm water. The water should flow freely out the outdoor termination.

5. 5

   Check and clean the drain pan

   Inspect the drain pan under the indoor coil. Wipe out standing water, slime, or debris with a towel. Confirm the pan slopes toward the drain opening so water flows out rather than pooling.

6. 6

   Restore power and test

   Replace the access port cap, turn the breaker back on, and start the AC. Go outside and watch the drain line termination—after about 15 minutes of running, you should see a steady trickle of condensate exiting the pipe.

Signs your AC drain line is clogged

• Water pooling around the indoor air handler or furnace.
• Water dripping from the ceiling or wall near the indoor unit.
• The AC shuts off on its own—a safety float switch may have tripped.
• Musty smell near the indoor unit or a visible slime in the drain pan.
• The system runs but humidity in the home feels higher than usual.

Why condensate lines clog

As warm indoor air passes over the cold evaporator coil, moisture condenses into water droplets that drip into the drain pan and flow out through the PVC line. Dust, pet hair, and airborne particles mix with that water, creating a warm, dark, nutrient-rich environment where algae and mold can grow.

Over weeks and months, that biological growth forms a slimy biofilm that narrows the pipe until water backs up. Homes in humid climates and systems that run constantly in summer are especially prone because they produce more condensate.

Prevent future clogs

• Pour a cup of distilled white vinegar into the access port every 1–3 months during cooling season.
• Replace air filters regularly so less dust reaches the coil and drain pan.
• Have an HVAC technician clean the coil and inspect the drain during annual maintenance.
• Consider installing a drain pan float switch that shuts off the AC before water overflows.
• Keep the area around the indoor unit clear so you can spot leaks early.

When to call an HVAC technician

• Water has reached drywall, insulation, electrical components, or the attic floor.
• The line is inaccessible, buried in a wall, or runs to a rooftop.
• You have cleared the line but water backs up again within days.
• The drain pan is cracked or the connection between the pan and the drain line is leaking.
• The system has a safety float switch that keeps tripping after clearing.

Common questions