Every year around this time I go through the effort of installing two air conditioners. They are identical units (Kenmore Model 580.76100), both purchased in the 1990s, and both very heavy. It's the heaviest thing I lift in the entire year.
Two things improved in how I've handled this yearly chore.
The first thing was to keep the upstairs unit upstairs. I don't remember when I started doing this, but it had to have been very early. When we first moved into our house, I kept both A/C units in the
basement, which resulted in me carrying one of them up two flights of
stairs! I now store the upstairs unit in a closet right next to the window its installed in. Now I only have to lift it up to the window sill.
The second thing was to use an old toy wagon to roll the A/C on the floor. Before, when I was younger and stronger, I could crab-walk the unit from the corner of the basement, up the stairs, then to our dining room window. This heavy lifting does a number on my back! With the little wagon, the only lift I do is up a single flight of stairs. Once upstairs, I take the wagon and roll the A/C to the window. I started using the wagon in five years ago.
Every year my technique for installing the air conditioners becomes more refined. I take notes. I use work gloves. I have become familiar with the unit's bizarre center of gravity, which helps in the lift. During the Olympics, when I watch weightlifting, I wish one of those competitors could help me when I have to mount and unmount my air conditioners.
I'll be exploring mini-movers to help with this task in the future. Or maybe I'll just find a home with built-in air conditioning.