Air Conditioning - Through-the-wall unit leaks water

I have an LG through-the-wall a/c, not sure of the model but it's around a year old. It began leaking water down my living room wall onto the carpet. I saw that in the back (the part that's outside the building) there was a big pool of water just sitting inside the wall sleeve. At first I assumed there must be a drain line clogged somewhere but I don't see a drain line at all. Now I think this unit was probably not designed to have one, but I'm not sure. There's certainly no hole in the wall sleeve on the underside, and no hose. There are a lot of slats in the sides and top of the wall sleeve, which I presume are for ventilation, and there is a fan facing the outdoors (but contained within the wall sleeve).

I cleaned the filter in the course of my "inspection," and it needed it, but is the filter alone enough to cause this problem? I looked through the product/installation docs for LG models that are available now, and although they're not the same model, I'm hoping the function is similar. Those docs don't mention any drain lines or holes, but I did see one that listed a drain valve in the schematics. I don't know that my unit should have one of these at all, but I sure can't find one from the outside.

This system worked fine for over a year so I think the installation angle is fine. My landlord is taking forever to respond on this, so if I can diagnose it and move on I'd be thrilled. I finally turned it back on last night (it's been 2 weeks since the leak) and when I left this morning I could see water outside (sitting inside the sleeve), but not as much as I saw when the problem occurred, and none was making it back in as far as I could tell. Should I anticipate a repeat performance? How much water is normal to be collecting out there? Am I correct in assuming this type of unit is drain line-less, or should there be a drain mechanism that I'm just missing?

Thanks!

I cleaned the filter in the course of my "inspection," and it needed it, but is the filter alone enough to cause this problem?

This sure can be it. that let the coil freeze. The unit should slide out . You can clean and check it there is a drain line like from the inside coil to the back outside coil. Can have dirt in it. If to much water it should run out the outside .

ED

Those wall units use the condensate to cool the condenser coil. If it has been pulling a lot of moisture out of the air it will over flow. If it was up to me I would make sure the sleeve is pitched away and drill a few drain holes in the sleeve as far to the end as possible, not the a/c unit it self. It is possible that the channel that the condensate flows through is backing up like ED said with dirt or what ever, take it out and wash it out with a hose and check the pitch of the sleeve with a level.