Heating and cooling systems are not simple machines. An air conditioner works by transferring heat in the home into a heat sink, and replacing it with cool air. It also has a large number of refrigerant lines that supply the cool air to different points in the house. With all of this, it's no wonder that the unit itself is so big.
This is why it's important to only hire a licensed HVAC contractor to do work on your heating and cooling system
. Someone without a license will probably not be able to deliver quality service. As a result, the problems your machine has might not get fixed, and in some cases will even grow worse.