How to clean small through the wall AC units?

I have a couple of small through the wall ac units. They are the 9000 btu single room style bought a discount type stores. Athought I clean the manufacturers filter routinely, it looks like quite a bit of dirt/dust is building up on the radiator? (coil?) directly behind the filter on the return air side. I am temped to blow it out with air, but that strikes me a maybe just driving it deeper. Is there a way to do this without removing the unit?
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You can clean the AC fins using compressed air if:
1) You use reverse air flow - shooting compressed air in from the clean side. If you can't get access to reverse flush, then you can experiement with hitting the fins at a very oblique angle - you are hitting the fins sideways. This isn't as effective, but better than nothing.
2) You don't smash the fins with high psi air. I use a special kind of blow gun with produces a very high volume of air with a much reduced psi. Available at Harbor Freight and other outlets for compressor items. The barrel of the air gun has openings at the base to entrain ambient air (suck in outside air) as the compressed air moves through the barrel. This entrained air greatly increases the volume of air and also slows down the airflow.
3) You lightly loosen the debris carefully with an old soft toothbrush or some other very soft brush. Obviously, you should brush with the fin direction and not against it.
I'd suggest picking up an inexpensive fin straightening tool (also available at Harbor Freight). Have it handy to touch up any areas where you accidentally smash the fins. You can also straighten them with an old knife, but thats pretty slow.
Good luck, Gideon
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Usually, no.
Blowing it out with compressed air is better than no service. but, if you want it really clean, you need to disassemble the unit and use professional coil cleaner.
I've cleaned out a LOT of window or wall units. Probably over 100 of them -- compressed air doesnt do it.
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I used to unplug the A/C unit and use a hand spray bottle filled with water. Holding the spray bottle 1" away from the fins - I would spray the fins starting at the top & working my way down. My theory was that the water would flush any dirt off the fins & there was no problem with the small amount of water used as the A/C units are designed to drain condensed water off the fins to the outside (provided it is installed correctly with a slight slope to the outside).
I would do the same to the exterior fins - but in that case using a garden hose. Amazing how much gunk collects on the fins over a season.
Let it sit for 1/2 hour to ensure the water is drained and away you go...
I also do this to my central air outside condenser unit each year - making sure I don't have so much water pressure that it would deform the fins..
Last spring, after much flushing of the fins I tried spraying the fins with some 'Siege' - which is a air filter degreaser chemical. MAN - there was tons of dirt that came off when I again sprayed the fins. I guess the dirt is not dislodged by just water alone. Because of this - it might help you to use a small (very small) amount of dish soap (or Siege if you have it) in the water you spray on the coils. Then rinse with clean water (you don't want your A/C blowing bubbles afterall.
By the way - Siege is also great for any type of cleaning you need to do around the house (and no, I'm not a salesperson for it - just a BIG fan of the product).

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