Spent my Sunday morning on the condenser coils and the difference is wild

I've got a 2009 GE side-by-side and learned the same lesson two summers back when the milk stopped staying cold. Mine were a bit diferent, the coils sit underneath and there's a fan back there that flings dust around, so half of it had ended up on the floor too. What worked for me was pulling the fridge out further than felt necessery, then using a cheap 2 inch paintbrush to loosen the matted felt before vacuuming. The vacuum alone just polished the surface, the brush is what got the clumps moving.

The other trick that saved me was slipping the cardboard tube from a roll of gift wrap over the shop vac nozzle. It fits down between the coils and pulls fuzz from deeper than the bare hose reaches. Worked better than the brush kit I bought first, and it cost nothing.

Mine hadn't been touched in prolly ten years, so it was worse than what you describe. Took me two sessions over a weekend because I kept having to empty the vac and let my back recover. Now I do it whenever I swap the furnace filter, roughly twice a year, so I don't rely on remembering.

One thing to check while you're back there is the drip pan. Mine had a stagnant puddle sitting in it that I only found because the whole kitchen smelled musty once the fridge moved. Rinsed it out with some diluted bleach and the smell was gone by the next morning.

My setup is the opposite layout, an older Whirlpool with the exposed coils on the back, so I never have to pull it far off the wall, just enough to lean it and get my arm behind. The dust on mine bakes on instead of sitting loose, especally near the bottom where the compressor heat bakes it into a crust. Vacuum alone did nothing on that crust. What finally worked was a damp microfiber cloth wrapped around my hand, wiping each loop individually like I was polishing pipe. It sounds tedious but the gunk comes off in one pass once it's damp, and I follow with a dry cloth so nothing is left wet. Took closer to an hour the first time, maybe 15 minutes now that I keep on top of it. I've got one long-haired cat and I do it about four times a year, ussually when I notice the condenser fan kicking on more often in summer. One thing I'd add for anyone with rear coils, check the drip tray above the compressor while you're back there. Mine had a soup of dust and a bit of spilled juice from a leaking bottle years back, and it smelled musty every time the fridge ran til I washed it out with dish soap and dried it. Now the tray gets a rinse every time I do the coils.

I do appliance side work on weekends, probably 15 or 20 fridges a year, and the thing that messes people up after a deep clean like yours is bent fins. If you went at it with any force, check the coil rows for fins flattened over sideways. A coil comb from any hardware store straightens them out in a few minutes and airflow matters almost as much as the dust removal. Bent fins choke the air the fan pulls across the condenser even when the coils look spotless.

Been doing this since the days when the coils sat on top of the box and you just wiped them with a damp rag twice a year. One thing I'd add is check the door gaskets while you're at it. A leaky seal makes the compressor run long even with spotless coils, and a dollar bill closed in the door tells you plenty. If it slides right out, the seal's shot. Also, unplug the thing before you shove it back in, those fan blades don't care about your fingers.