What is causing water to drip inside while using air conditioner?

Answer 1

The act of cooling air also removes humidity, which causes condensation. Just like a window unit on a house does on a humid day, your car's air conditioner causes condensation as warm humid air passes over the cooling element (the evaporator). Your car should have a drain tube somewhere underneath where this fluid normally drips out - you can see the puddles on the ground from your car and others at a stop light, usually. This drain tube is almost always on the passenger side or near the center of the car. It's usually around 1/2 inch diameter, and may or may not have some kind of baffle on the end to keep misc stuff from entering.

If you have water dripping inside your car, there are two basic causes. One is a plugged drain tube, which is very common (because no one ever cleans those things). Figure out where the A/C drain tube is on your car, and you can probably clean it out with a chunk of wire or something like that. There's probably info online with a quick search. The other related problem is that you may have a crack somewhere in the evaporator housing allowing the condensation to drip out before it gets to the drain tube. This may or may not be exacerbated by a plugged drain tube. Again, where this could be located is dependent on your specific vehicle.

A competent mechanic should have no trouble helping track this down, and from a cost perspective, it should not take more than an hour or so to resolve a plugged drain tube. If you have something broken in the interior, it could be much more expensive to fix, as it may be anything from a simple repair to something which requires disassembling the entire dash (which could be close to a full day's work in the worst case).