How to Stop Condensation Under the Car Mat

by Richard Rowe

Condensation under your car's floor mats is a two-part problem with a single solution. Heat under your floor mat comes from the exhaust pipes, and causes moisture trapped in the carpet to steam and collect on the bottom of the mat. The moisture under your carpet has to come from somewhere and that somewhere is almost undoubtedly the air-conditioning system. Normally, condensation in your AC system exits through a small drain tube in the bottom of the vehicle, but over time that drain tube can get clogged and cause water to backflow into your car interior.

Kick a set of wheel chocks in behind your rear wheels. Slide a jack under the front of your vehicle, center it on the frame and lift the car enough so that you can crawl underneath. Secure the frame on jack stands and slide underneath.

Look for your air-conditioning system drain tube under the passenger-side of the vehicle where the bulkhead meets the floor. The drain tube varies by vehicle; some use a 1/4-inch diameter hard plastic tube, others use a large rubber tube. Some tubes stick straight out of the floor, others are wound up in a semi-circle and still others are recessed into the floorboard and surrounded by a concave opening.

Clean the tip of the tube out with your screwdriver, hitting it with a quick spray from a garden hose to dislodge any encrusted dirt. Once you have the surface dirt out, straighten out a coat hanger and push it into the tube. If the spiral ends of the wire will fit into your tube, then you're in luck; this screw-shaped spiral acts like a Roto-Rooter to remove clogs. If it won't fit, snip off the spiral and push the wire through.

Work the wire up the tube in a back-and-forth motion to knock any clogs loose and then pull the wire out from time to time to remove the debris. If you were able to fit the spiral wire into the tube, turn the wire in a clockwise direction to "screw" the spiral through any clogs. The tube should be about 12 to 24 inches long; once you get that far in, you may hear a muted tap as the wire contacts the bottom of the heat exchanger.

Pull the wire out, drop the car down off the jack stands and start it. Turn the AC on full and allow it to run. Within a few minutes, you should see water start to drip out of the drain tube. To finish the job, take the car to you local car wash and use a wet-dry vacuum cleaner to pull the remaining moisture out of the carpet. Leave the mats out for at least a week to give the carpet time to dry.

Tip

  • check In really severe cases, water puddled under the carpet or soaked into the insulation can take several weeks to completely dry out. The worst case scenario is that you'll need to pull the carpet out, replace the saturated section of insulation and dry the floor with a towel.

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About the Author

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.