838 HVAC Operation: Whenever the engine is operating, the pulley is rotating since it is connected to the crankshaft by a belt, but the compressor does not operate until the clutch is energized. When the air conditioning system is switched ON, the ECU generates a signal for energizing the compressor. The electromagnet attracts the pressure plate and pulls the plate against the friction facings on the pulley. The friction between the facing and plate causes the clutch assembly to rotate as a unit, and drive the compressor. COMPONENT DESCRIPTION OF HVAC / A/C SYSTEM : Compressor It is the heart of A/C system specially designed to compress the refrigerant. The compressor draws vaporized refrigerant from the evaporator. It compresses the refrigerant (resulting into temperature rise of refrigerant) and the refrigerant will be passed onto condenser for condensation. Compressor relay Compressor relay is located in fuse box which is used to operate the compressor magnetic clutch. The magnetic clutch continues to operate as long as air conditioner is under operation. Once the air conditioner is put in OFF condition, the compressor relay gets cut off and the magnetic clutch gets disengaged from the compressor. The cut - in and cut - off of relay is governed by ECU. Magnetic clutch A magnetic clutch is used to connect and disconnect the compressor from the engine. Main components are stator, rotor, and pressure plate. Principle: When the current is fed to the coil (as shown fig. on the right), magnetic force is generated in iron II which attracts iron I. Construction: A magnetic clutch consists of a stator, rotor with pulley, and pressure plate to engage the drive pulley and compressor magnetically. The stator is fixed on the compressor housing, and the pressure plate is attached to the compressor shaft. Two ball bearings are used between the inner surface of the rotor and the front housing of the compressor.
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