Best angle to tilt a through-window air conditioner

According to this, the Frigidaire FAS182H2A1 is an 18000 BTU device.
http://www.appliancepartsnationwide.com/FAS182H2A1/53279.htm

That's pretty powerful if working properly. The government suggests 8000 BTU for 325 SF.

http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized

Check your outside coils too and clean if needed. If that is not a problem it could be something internal. Some examples:

1. partial clog in your expansion valve.
2. low freon level

If cleaning the outside coils doesn't work, I do not expect repair to be practical. You can buy a new 10,000 BTU unit from Home Depot for $300. It would be reasonable to ask the owner to pay for it.

1 verify that there is a slight slope downwards in the drain pan. the manufacturer usually specifies how much. 1-2 degrese i believe so that the water naturally drains away from the house and out the back of the ac unit or gets hit by the rear fan and spashes on the external radiator for extra evaperative cooling. they may have left some corner or such open just enough to let the water drain under the foam from the front section in the house to the rear one outside.

2 if it has an eco/auto mode where it will activly evaperate the water use it if possible. running the unit at full blast for long stretches will build ice on the inside and outside coils, usually outside first. keeping the temprature in the room constant instead of large swings every few hours should help some to.

3 verify in house humidity is not high you will get more condensation and possibly mold problems from it. you will have to verify but i think 40% or so is about as high as you want it.