Rick's Free Auto Repair Advice

Clogged AC condensate line drips water on carpet

Fix clogged AC condensate drain line

How the AC condensate drain line gets clogged

As car AC systems work to cool the air, moisture from the air condenses on the cold evaporator coil. The condensate drains out the bottom of the heater box onto the ground. However, when the system is set to FRESH AIR, it’s drawing in outside air that contains mold spores and bacteria. The mold and bacteria settle on the the water soaked evaporator coil and grow, especially when the vehicle is turned off and the cabin heats up. That’s when the mold, mildew and bacteria flourish to form a stinky slime that multiplies, that smells like dirty socks. The slime can also drip down and clog the condensate drain line. Once that happens, the condensation can no longer drain out of the heater box, so it leaks out onto your passenger carpet.

clogged condensate drain

How to unclog the condensate line and kill the smell

What you’ll need to unclog the condensate drain and get rid of the slime

Old towels
A can of compressed air
Pipe cleaners
A can of Kool-It Evaporator and Heater Core Cleaner

Kool it cleaner

Kool-it AC and heater cleaner

Step 1 Disconnect the drain line and drain out the water

• Locate the rubber drain line coming off the heater box on the passenger side of the vehicle.
• Lay towels directly under the drain to soak up the water and slime
• Disconnect the rubber drain line and allow the water to drain onto the towels. Wash the towels afterward with Lysol or other bacteria killing solution

Step 2 Clean out the drain line

• Run a pipe cleaner drown the rubber drain line to open it.
• Run the pipe cleaner up into the heater box to open it
• Spray compressed are into the rubber drain line to blow out any remaining debris

Step 3 Kill the mold, mildew and bacteria on the heater core and evaporator using Kool-It

The vehicle shown below recommends injecting the Kool-It treatment from under the vehicle. However, you can also inject it directly into the heater box from inside the passenger cabin

• Insert the tubing into the heater box and press the button on the can.
• Inject the entire contents of the can into the heater box
• Remove the tubing and immediately reconnect the rubber drain line.
• The product will foam up, expand and coat the entire evaporator coil, killing all the mold, mildew and bacteria.
• Allow the foam to work for 15-mins, during which time it will turn back into a liquid and start draining out the condensate drain.
• After 15-min, turn the blower fan onto the lowest setting and let it run for 5-mins.

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Posted on by Rick Muscoplat

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