A mini-split has an indoor head on the garage wall and a small outdoor unit, connected by a refrigerant line through a small hole. There's no ductwork, and you never have to open the garage door. The U.S. Department of Energy's Energy Saver guide covers how ductless systems work.
What the installer should look at
Heat load
Square footage, ceiling height, insulation, door type and which way the garage faces.
Unit placement
Where the indoor head blows, and where the outdoor unit can sit with good airflow.
Electrical
Panel capacity and the run for a dedicated circuit.
Condensate
Where the drain line goes. In the desert this is a small amount, but it still needs a path.
Related: insulation & insulated doors · other garage AC options
FAQ
Will a mini-split keep my garage cool in July?
It can make a big difference, but results depend on sizing, insulation and the garage door. An uninsulated garage with a west-facing metal door is a tough space to cool. That's why installers often suggest insulation along with the unit.
Does a mini-split also heat?
Most mini-splits are heat pumps, so they can heat as well as cool. Ask the installer about the model's heating mode.
Do I need a new electrical circuit?
Usually yes. A mini-split typically needs its own circuit. The installer should check your panel during the visit.