The air conditioner compressor is the heart of your cooling system.There are basically four types of compressors that are used in air conditioning systems. A rotary compressor is commonly used in window units and some central ac units. They have been around for many years and are inexpensive and durable. A reciprocating compressor is the most common in lower efficiency split air conditioners. They are relatively inexpensive but not as durable. A scroll compressor is the most common type in higher efficiency equipment. They are very durable and efficient but are typically more expensive. The latest innovation is variable speed compressors which are commonly referred to as inverter drives. These are in the top of the line high efficiency units.