Passenger-side wet carpet is most often the AC evaporator drain or a leaking heater core. Both are behind the dash on the passenger side. Here is how to tell which one and what each fix costs.
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Most cars route the AC drain to the passenger side of the firewall. When it clogs, condensation pools right under the glove box. Wet only after AC use is the signature. Cost: $0 - $50. DIY: Easy. Severity: Low.
Get a Free AI Diagnosis →On many vehicles the heater core sits behind the passenger side of the dash. A leak drips sweet-smelling coolant onto the passenger carpet, fogs the windshield, and slowly drops the coolant level. Cost: $300 - $1500. DIY: Hard. Severity: High.
Get a Free AI Diagnosis →Leaves and pine needles in the cowl panel under the wipers block the drains. Water overflows into the HVAC blower box and ends up on the passenger floor. Cost: $0 - $30. DIY: Easy. Severity: Low.
Get a Free AI Diagnosis →After a windshield replacement that did not seal at the corner, rain runs down behind the dash and onto the passenger carpet. Wet only after rain. Cost: $150 - $400. DIY: Hard. Severity: Medium.
Get a Free AI Diagnosis →A cracked plenum or a cabin filter door that does not seal lets water that should drain outside come inside instead. Most common after rough fall storms. Cost: $50 - $200. DIY: Medium. Severity: Low.
Get a Free AI Diagnosis →Before paying a shop, run this short check. About 80% of these issues come down to a blown fuse, a tripped circuit, or a stuck switch.
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Shop vac the standing water first. Park in the sun with windows cracked and run the heater on full blast (AC off) for 20-30 min a day. A small dehumidifier in the car overnight speeds this up.
Usually yes - $700-$1500 because the dash often has to come out. Some pickup trucks and older cars are easier ($300-$600). Always get a written estimate.
Yes - it is one of the easiest DIY repairs. A 3-foot piece of weedeater line, a coat hanger, or a quick puff of compressed air at the firewall drain almost always clears it.
None - a sealed system should not drop noticeably between services. Anything more than a half-inch a month with no visible external leak points at the heater core.
Yes - mildew under a wet carpet causes allergic reactions and respiratory issues. Pull the carpet padding and dry or replace within a week.
A poorly seated cabin filter or a cracked filter housing can. Make sure the filter door clicks shut and the filter is right-side up.