Most of the ones I do are carried into the shop. I have a couple of customers with 25,000 Btu units I pull once a year and clean.
They are a pain to work on, but I'm in one of those niche markets. I do warranty work for a couple of manufactures so I get a few calls on them.
The smaller units don't even have parts listed for them anymore. They are a trade out warranty or a throw away after the first year.
I can't give a step by step to take one apart. It depends on model and manufacture. Just pull it out and look. You should see pretty quick what you need to remove.