I recently bought this coil brush for a few bucks and I used it to clean the coil behind the filters on one of those portable AC units and it was absolutely amazing. Then I did two others and it was very satisfying. It didn't look too bad but I got big clumps of hair and crud out. I would love to use that foam and water on them but idk if they are designed for that. Soon I'll be trying to clean my car's AC system through the drip tube/hole by spraying coil foam and a bit of lysol in there.