What causes a wet passenger seat carpet?
A leaking heater core, plugged AC condensate drain, plugged sunroof drain or a leaking windshield can cause a wet passenger seat carpet.
Diagnose the cause of a wet passenger seat carpet
First, find out what type of liquid you’re dealing with. Wipe your finger on the carpet and slide your index and thumb together. If the liquid is slippery, that’s engine coolant and there’s only one source for it; the heater core. Replacing the heater core in most late model cars and trucks requires AC evacuation and complete dashboard removal. You can try a stop leak product as long as you follow the directions to the letter. Don’t overdose the system or you’ll wind up with even bigger problems, like a clogged radiator! For more information on stop leak products, see this post
If the liquid isn’t slippery, it’s a water leak caused by a plugged AC condensate drain, plugged sunroof drains or a windshield leak. If you notice the wet passenger carpet right after a heavy rain and you’ve got a sunroof, chances are you’ve got either a clogged sunroof drain or a leaking windshield.
Diagnose and fix sunroof drain
All sunroofs are built with drains to handle any water that manages to get past the gaskets. The drain tubes route through the left and right front pillars and through the two rear pillars. To check the condition of your sunroof drains, open the sunroof and locate the drains. Look for debris clogging the drain. If you see debris, remove it with a vacuum. DO not try to push the debris down the tube using a coat hanger or air pressure. The drain tubes are made with flexible rubber and a coat hanger can poke a hole in the tubing, making your leak problem even worse.
See this post for tips on the best way to unclog a sunroof drain
Once the drain is cleared, simply pour water down each drain and check for puddles under the vehicle. If you see puddles and the carpet doesn’t get wetter, you’ve fixed the root problem. Then you’ll need to dry out the carpet. See this post.
Diagnose and fix a clogged AC condensate drain
If you experience a wet passenger carpet right after using the AC system, chances are the condensate drain is clogged. How does it get clogged? From bacterial slime. Your car’s AC works by removing heat from cabin and outside air. As that air flows across the AC evaporator coil, moisture condenses on the evaporator fins and flows down to drain and out to the bottom of your car. When you shut off your car, the interior of your car heats up from the sun. The AC evaporator coils are still damp from the condensation and the bacteria in the air starts to grow on the fins, creating a bacterial stew that’s slimy. That slime eventually falls to the bottom, forming a plug.
With the drain now clogged, future AC use creates more condensation and that water overflows through the heater box joints, falling onto the passenger carpet.
To clear the clog, you’ll need several old towels, a can of compressed air and a can of bacterial treatment.
Locate the drain tube at the bottom of the heater box. Lay the towels under the drain. Detach the drain from the heater box and let all the water drain out onto the towels. Remove the towels when the water stops flowing.
Blow out the drain tube using the can of compressed air.
Attach the tube from the can of bacterial treatment to the heater box drain port and inject the entire can of treatment into the heater box. The solution will foam up and coat all the evaporator fins, killing the bacteria. After injecting the solution, attach the condensate drain tube. The foam will do its job, turning the slime into a liquid and all the solution will drain onto the ground. The treatment usually lasts a year. Then clean and dry the carpet to prevent mold and mildew. See this post
Diagnose a leaking windshield
I’ll be honest with you, this is harder than it seems. Worse yet, fixing a leaking windshield isn’t really something a DIYer can do easily.
But if you’re game, here goes.
Move the car outside and near your garden hose.
Peel back the wet passenger seat carpet and padding. Dry the floor and interior firewall area with old towels.
Next, attach a garden hose nozzle and adjust to the strongest stream. Staring on the passenger side of the vehicle, aim the spray at the bottom of the window and cowling under the windshield. Do not spray the upper portion or the driver’s side at this time. Stop spraying and check the passenger floor and firewall for signs of water. If you find water, you know you’ve got a leak between the windshield and cowling.
To find the exact point of entry, remove the wiper arms/blades and the cowling. Add food coloring to a gallon of water and pour the water in the gap between the windshield and cowling. Check for colored water inside the cabin. If you don’t see a leak, mix a different color with water and pour it into the cowling. Check for leaks. Based on the color of the leaking water, you can nail down the source of the leak. If you don’t see water from any of those tests, repeat the same process on the driver’s side.
Then repeat the entire process from the top of the windshield.
Fix a leaking windshield seal
If you find that the windshield to pillar or cowling seal is leaking, take it to a automotive glass installer. Trust me, all your DIY fixes will fail.
©, 2018 Rick Muscoplat