Is air conditioning contents or buildings?

A permanently connected

A split unit with an indoor part, an outdoor unit and fixed pipework is a permanent fixture and therefore structure. The outdoor unit belongs with it, even though it hangs on the facade.

Report the installation to your insurer. It raises the rebuild value, and anything installed since your last declaration is often not covered.

Portable

A movable appliance with a hose through the window is contents. You can take it with you and it is not fixed to anything.

What is and is not covered

Damage caused by an external peril: fire, storm, lightning strike: is covered, as is theft or vandalism of the outdoor unit. The latter happens more often than people think.

A an internal breakdown is an inherent defect and falls outside the buildings insurance. For that, the manufacturer's warranty or a maintenance contract is the route.

In a flat

An air conditioner you had installed yourself is owner's interest, and for the outdoor unit you usually need the VvE's permission. Without that permission, removal can be demanded.