A/C compressor is the heart of an A/C system. The compressor is driven by a belt attached to the car engine. This is where the low-pressure refrigerant gas is compressed into a high-pressure, high-temperature gas before being pumped to the condenser. A fully functioning compressor is necessary for the air-conditioning system to provide peak performance. Compressors can also leak refrigerant, resulting in less cold air going into the interior. Internal parts can also fail, leading to no cold air. Refrigerant is pressurized by the air compressor, which senses the temperature in your vehicle and makes desired changes when activated to do so from the center console. Symptoms of a failing AC Compressor includes diminished air flow, warmer air, rattling noise etc.