Air conditioner draining into back of car

We have a 2008 Buick Lucerne. Now that the weather has become humid, we have been using the air conditioner more. We noticed that the carpet was wet on the rear passenger floor. Shortly after that, we noticed it on the driver rear floor. The dealer repair guys are puzzled and say it can’t be the air conditioner as it would get the front passenger floor wet and not the back. They blamed on a luggage rack or sun roof (which we do not have!) or on the rain or car wash. We haven’t been through the car wash and it hasn’t rained here in over 3 weeks. What would cause this to occur and how do we fix it?

Have them check the condensation drain at the firewall for blockage.

The evaporator core for the AC is located at the center of the dash board on your vehicle. If the drain is plugged, water accumulates in the drain pan and overflows onto the firewall. This water can then run down the firewall into the channels under the carpet collect on the floor in the back seat causing the carpet to become wet.


Unless it has been raining a great deal the shop should check the evaporator drain before making any presumptions. Are you able to look under the car, @Sharr?

Two dealer mechanics were stumped because they couldn’t understand how water could get to the back of the car and not soak the front passenger floor. We brought the car to our local neighborhood mechanic. They unplugged the drainage hose and fixed the problem. And the cost was less than $20.00! Thanks for responding to my post.

Be sure to dry out the carpet well. You may want to go to a detail shop and have the carpet removed. Water trapped under the carpet may cause rust of the floor panel and also could cause mold.