How do I easily clean the inside of air conditioners?

Are you talking about window units or a central unit?

I've been having really good luck using a steam cleaner. It is chemical free and easy to use. I have this one and love it: https://amzn.to/2UYwk7w (affiliate link)

If you mean the HVAC supply vents and return grills. I use a duster or paint brush to rempve the surface dust first. Then just wet down a sponge in soap and water and wipe them clean.

The correct way is to buy a coil cleaner from a HV/ac supply company such as United Refrigeration then a good set off rubber glpves and eye protection. Now you must mix this with water for it is concentrated ( i use 50/50 solution ). Get a sprayer from Home Depot ( garden section ) and mix it in the sprayer's container. Then take the cover off the A.c. codenser ( inside unit ) spray the coil and let it sit fro 10 or 15 min rince with clear water ( apply with sprayer ) and check with a flash light to se if unit is clean. You should see the light on the opposite Side of the coil. If you dont then repeat the process until you do. Tjis will not only get rid of dist and dander but it will help with your electric bill quite a lot. It is also good for your health and that off your family. PS change the filter on a regular basis( i do it on the first of every mouth ) and still clean the coils every year inside and out. Why you ask because thats what i do for a living and i know how much it helps. Keep cleaning