German Shepherd Dog.
At least once a month. BTW if the rear is closed the air comes in the front under the doors. Dog hair will clog it up. Love my dog but when he's gone I'm done with dogs
Spring & Fall.
Blowing out from under the units also.
Condensation coils for the A/C get cleaned, evaporation coils in the house need a chemical cleaning at least once a year, it's amazing the oily mess that can build up on them.
I'm off grid so I track the power everything consumes and clean coils make a HUGE power use difference.
For the last couple of decades they've been putting them on the bottom. I don't know every fridge out there, but... double check? Normally it's deep freezers that run the coils all over just under the skin. ETA: Researched this, and now it appears the coils are interior to the compressor compartment with air passages so they can't be cleaned.
Speaking of... Mine are the bottom, and get nasty, and I almost never do them. Last time was when I moved 4 years ago. This is my fridge and it sits on carpet (sat on carpet in the basement of the old house too), but this time I did it a favor and put an office chair roller plastic thing under it so it can breathe a little easier.
I have a vacuum attachment that reaches into the coils on the bottom and just use a brush attachment for the back. It fills with cat fur so I check it and clean it every time I change the water filter, about every 6 mos.
I put a return air grill behind mine since it buts up to a hallway to allow for better air flow. Ours is a pita since the previous ownwr was an idiot and did not lay flooring under it
My refrigerator has coils in the bottom. I use a refrigerator/drier vent brush about every other year.
Then vacuum up the dust. I also clean any gunk off the fan blades while I'm at it.