Never mind. Someone told me to open the front grill to check the coils, which i did. They had black wet caked-in gunk. I used skewers & toothpicks for hours (also thin pins) and now my fingertips feel prickly pain.

I'll see what happens, but in any case, there was extreme rust inside. Really horrible. Time for a new one.

Sounds like (and appears per your first picture, the 2nd isn't clear) that there's no air filter in the unit. Supposed to be a filter in the front panel (cleaned as needed so airflow isn't impaired) to catch dust from getting into the evaporator coil. Your model is factory-equipped with a mesh filter that slides in/out of a slot on the right side.

Frigidaire Part Number 5304525534

You can also get generic foam filters cut-to-fit but they're too flimsy to slide into the slot ... would have to remove the front panel and attach it directly, remove for cleaning.
Frost King A/C Filter

Actually it did have a filter which i cleaned regularly.. I just bought a new AC today, practically identical, though different model number. The seller delivered it and installed it in my window. Upon removing the old one (pictured above), it was sloshing and dripping loads of water onto the floor, which i needed to mop up. When i peeked thru the overhead vents, it looked like a mini swimming pool at the bottom of the AC. The appliance seller told me that's not normal. I've no idea where it was coming from. The extreme wet weather of these past years, combined with it being 27 inches from the East side of the house? Or something else?

All ACs produce condensate water. Normal installation tilts the unit to the rear slightly so the water can drain out. Over time if dirty, the drain holes get clogged. And you get water everywhere.

I see, thank you both for explaing!

I have a followup Q along with attachment. I first need to make a correction. See, i had thought my new one is identical to my old one. But i now see that, even though they failed to picture it in their diagrams, the underparts of their various models are not identical (I went outside and checked to see if the new one is dripping - which its supposed to do - but i didn't see it dripping. Yet the guy assured me by phone today, that he made sure to put it at an angle, and that he knew that's required for drainage.

Whereas my other (original) one, which is at my other window, was indeed dripping. This new one has a much smoother bottom than the old one, and unlike the old one, doesn't have a hole near the outer edge.

Again, i emphasize, on the new one i do not see a hole near outer edge, unlike the old.

Perhaps the new drain-hole is at the more inner-area that's directly resting on the metal outer rim of my 1950s wood windowsill? (see attachment) But why on earth would they redesign it that way, rather than leaving the hole near the edge? Shouldn't they realize the risk of it draining into the wood sill and developing into a swimming pool on the sill?

The old one is FRA052X17

The new one is FFRA051WA1

When i tried phoning Frigidaire for explanations on this difference, it was "non-service". A nightmare of long phone waits, followed by ignorance, transfer to the wrong supervisor in their hierarchy, non-accountability and rudeness. "Maam it's not my fault that he transferred you incorrectly". When i tried phoning again later, a msg stated nobody's available. The times we're living in are hell. Civility is dead. :-(