How to improve the air cooler

First, realize that with a single zone system and multiple floors, it's difficult to get the temperature correct everywhere. Also, since you mentioned this was an attic space, you're likely against the roof and getting heat from every wall plus from the computers and people in the space. In short, you're fighting a losing battle.

I've got a similar challenge, though not to your extreme, and here's what I have done. First, learn how to adjust the baffles on the ducts. In the summer, you want as much as possible going to the high floors, and the reverse in the winter. Get someone to feel the air coming out while you're pushing the baffle all the way to one side or another. For me, it made little difference until I pushed it all the way.

Next, exclude any rooms you don't need to heat/cool, e.g. a guest room or storage space in the basement. Shut the door and close the vents to reduce the effort you're putting on the HVAC.

Finally, I swapped out my return grille with models that accept a filter (they are hinged and open after releasing two small clips). These return grilles are special orders from the big box stores, but they carry them. I still leave a thin blue "rock catcher" filter directly on my HVAC blower itself. And I put a filter in every return except the upstairs in the summer and downstairs in the winter. The idea being to suck out as much air as possible from location that needs it.

This means that switching between heat and cool is a process, flipping the baffles and swapping in and out filters. But a little effort is better than a lot of sweating.

One last suggestion, since it sounds like you're running a small server farm in your attic. Either move that down to the basement, or consider replacing the window unit with a ductless mini-split system. You get to see out the window, and these systems have configurable thermostats.

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.