Question

Air conditioners are generally fitted at higher level on the walls of the room

Answer 1

[ hot air always present in atmosphere at the top.because, the molecules of hot air are lighter in weight.therefore they has less gravitational force.]
1)HOT AIR TRAVELS FROM LOWER LEVEL TO HIGHER LEVEL.

[Cold air contains water molecules means it is heavier in weight then hot air.therefore it has high gravitational force.]
2)COLD AIR TRAVELS FROM HIGHER LEVEL TO LOWER LEVEL.

From conclusion 1and 2 I think u understand why AC fitted at the top of the room.

Answer 2

Air conditioners are fitted at a higher level in the room because the air molecules get cooled and sink towards the floor. The warm molecules from near the floor rise upwards.

This process continues and results in effective cooling of the room.