So my window unit was basically a block of ice and I had no clue

I actually went through something similar last year, but it wasn't the dust buildup. My unit, a Carrier, started running through the middle of a really humid July when the outdoor temperature was only eighty-five degrees. I figured it was just a hot day, so I kept the thermostat set to seventy-two. After about five hours, I noticed the air coming out of the registers felt damp, not just cool. I stepped outside and saw the metal coil on the condenser unit had a slight layer of ice, which was strange since it was running outside.

I stopped it right away. When I looked at the operation settings, I realized the fan was on 'auto' and it was cycling on and off too quickly. I tried setting the fan to 'on' and adjusting the temperature down to seventy-eight. That seemed to help pull the unit through the worst of the damp cycles, but it didn't solve the issue completely.

Your instinct about the refrigerant was right though. Even after doing the cleaning, I eventually called a service tech because the unit would ice up again after about a month of good operation. They found a tiny leak near the coil connection and topped it off. It's frustrating when you think it's just a simple maintenance thing, but sometimes it's something deeper than the filter.

I had a similar situation last summer with my AC unit, but the problem wasn't inside the house like the filter. It was the exterior condenser unit sitting in the garage. The squirrels must have nested near the compressor, and all the yard debris and pine needles blew in. I hadn't realized how much obstruction there was until the compressor started making a relly loud, rattling sound. It was running, but the air was lukewarm at best.

After carefully clearing all the leaves and fluff from around the coils and the fan blades, the performance improved dramatically. It wasn't even about the airflow blockage in the ductwork, but rather the heat transfer on the outside unit being totally smothered by that debris. It felt like the AC was trying to breathe thru a thick blanket. The temperature dropped back down to a comfortable 72 degrees within a couple of days of that cleanup.

So while a clogged filter is definately a common culprit, sometimes the issue is external to the home and just needs a good clearing. Just make sure the ground around the pad is clear of tall grass and anything that could pile up right against the bottom of the unit.

One thing I learned the hard way on my window unit: even with a spotless filter, the blower wheel itself can get caked with grime and cut airflow almost as much as a dirty filter. Worth a peek if it ever ices up again despite the cleaning. Also, if you want to check whether it's actually fixed, hold a cheap thermometer at a supply vent and compare it to the air at the return grille. A healthy unit should show a clear drop between the two readings, and a weak drop points toward refrigerant rather than airflow.

This thread is making me side-eye my own setup. I close the vents in the spare bedroom and the guest bathroom because I figured why cool rooms nobody's in, but now I'm wondering if that's the same kind of airflow problem just in a sneakier form. Mine hasn't frozen up yet but the big vent in the hall doesn't blow very hard anymore. Is closing off a couple of vents a bad idea then?

Been around these things since the window units you hauled up a ladder yourself, and one thing I learned back then: after the frost is gone, run the fan only for an hour or so before you start cooling again. Dries the coil right out. Also check that the unit tilts slightly toward the outside. My old service guy showed me that trick with a level and a shim, because a unit sitting level or tipping inward holds water in the pan, and damp metal plus dust is a recipe for it happening all over again. Couple degrees is all it takes. Easy to overlook when you're staring at the filter thinking that was the whole problem.