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Compressor clutches are components that can be found the air conditioning (A/C) systems of cars, trucks, and other automobiles. These devices are a form of electromagnetic, or electro-mechanical, clutches, which means that they are operated by electricity but facilitate the mechanical transfer of torque. The function of a compressor clutch is to allow the pump inside a compressor to freewheel whenever the air conditioning is not in use. When the air conditioning is turned on, and the compressor needs to operate, an electrical signal is sent to the compressor clutch. This causes an electromagnet to turn on, which activates the clutch, and mechanically connects the pulley and pump together.
Automotive air conditioning systems consist of a few main components, which include a compressor, receiver/dryer, condenser, and evaporator. The system is charged with a refrigerant, which is pumped and compressed by the compressor. Compressed refrigerant gas then passes through the condenser, where it cools down and turns into a liquid form. That liquid refrigerant then passes into an evaporator, where a blower motor is typically used to cool down the interior of a vehicle. Since the compressor pulley is constantly rotated by an accessory belt that is typically connected to the crank pulley, a compressor clutch is necessary in order to turn the system on and off.
Unlike most other belt-driven accessories, automotive air conditioning compressors have two part pulleys. During normal operation, the main pulley of an air conditioning compressor will simply freewheel since there is nothing to mechanically connect it to the pump. When the air conditioning system is turned on, an electric signal is sent to the compressor clutch. This engages the clutch by activating a cylindrical electromagnet within the pulley and clutch assembly. The compressor clutch then provides a physical connection between the pulley and the pump, allowing torque to be transferred from the crank pulley.
When a compressor clutch fails, it will typically no longer engage. Compressor clutches can be replaced separately from the rest of a compressor, though this is not typically recommended due to the potential for other components to fail. If the refrigerant in an air conditioning system is low, that can cause a clutch to engage and disengage sporadically. This condition can usually be remedied by simply unplugging the wire that connects to the clutch if the expense of actually repairing the system is too high. In some cases, a vehicle may idle poorly when an air conditioning compressor clutch engages, which is typically due to the extra load imposed by the pump.