All air conditioners on all cars have a drain hole. Most even have a small tube attached to it. It allows condensation that gets built up on the evaporator to drain to the outside of the car. If that drain gets plug, it will drain inside of the car instead. If you take a clotheshanger get under the car and locate the drain. Look for a small tube. On most cars it's located on the passenger side of car. Run the clotheshanger up the tube work it around to loosen any debre. I would suggest to run your air for a few minutes first so you can verify any drianage. If that doesn't cure the problem and you've cleared the drain then your evaporator housing could be crack or some kind of seal may be bad. Like perhaps a two part housing that has a bad seal.
if that doesn't work it's probably a bad heater core and will need replaced.
I believe I might have a good answer for this. This came out of Alldata. You need to install the new Wiper Pivot Shaft Grommets, part numbers MN154877 and MN154878 for the drivers side. These will keep water from entering the blower motor. Water entry can cause blower motor failure. This problem affects 2002-2003 lancers. The technical service bulletin is 0351001.
because of condensation
on mine it is under the bed in front of the water tank and can be accessed from the door inside the trailer in the front of bed. It is just to the right inside that compartment
COULD BE PLUGED DRAIN
That is not very likely . Much more possible is a leak in the heater core.
in the glove box or under the seat
The 2004 has quite a history with that problem. The cowl under the wiper blade is probably warped allowing water in. That water also poses problems for the blower motor which is located right behind the glove compartment.
they live by breathing under water
Inside the Holland tunnel. Inside a submerged submarine.
It will be located under or behind the glove compartment. The rubber tube goes thru the firewall. Here is where they get clogged and leak water into the passenger side floor. Can be blown out with shop air from underneath or pull it in and dig out the clog.
I believe that the airconditioner condensation drain is plugged. How do I clear it?
Only if the water restrictor is worn out in the heater core fittings. It is made to slow the water up so it don't make that noise.