The electromagnetic clutch is the part that allows us to connect the A/C compressor to the engine using drive belts like a V-belt, Poly-V belt or a coupling.
By engaging the electromagnetic clutch, a part of the torque generated by the engine is transferred to the compressor enabling it to raise the pressure in the A/C circuit
The electromagnetic clutch consists of three parts:
- Electromagnetic coil: which is a spiral coil, made of conductive materials. Its characteristic is that it can generate a magnetic field from an electric current. It is fitted to the compressor with bolts or a Seeger ring.
- Pulley: through a sealed bearing, which is placed in a hub on the compressors shaft is allowed to rotate. It is dragged by a belt driven by the vehicle’s engine crank-shaft pulley.
- Plate: a disc placed in front of the clutch, fixed to the compressor’s shaft.
Function of the electromagnetic clutch: while the A/C system is not in use, the pulley of the compressor, (linked to the engine’s pulley with a dive belt) is spinning freely. When the A/C is activated the coil is crossed by electric current and generates a magnetic field. The magnetic field will attract the plate to the pulley, engaging them to rotate together and initiate the compressor’s function.
Clutch with limiter or coupling with external command.
A clutch with limiter is installed only in the variable displacement compressors. Compared to the electromagnetic clutch, it is not equipped with an electromagnetic coil. It has a pulley which is fitted with absorbers to the plate; therefore it is directly coupled to the compressor. It is clear that it is constantly engaged, even if the air-conditioning is off. It is because of the variable displacement, that the output of the compressor is reduced or increased.
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Function of the clutch with limiter at external command: The clutch with limiter, always being in direct drive with the vehicle’s engine, cannot be controlled.. Therefore, the control valve mounted in the compressor determines the displacement of the compressor based on the request of the A/C system ECU, through modular pulses (PWM).
How can the displacement be modified? The A/C ECU calculates and sends a signal which determines the action of the control valve. Depending on the values, the control valve determines the inclination of the plate, on which the pistons of the compressor are attached, and as a result the displacement and therefore the output of the compressor are altered.
Every manufacturer of A/C systems is using a specific clutch according to the specifications of the system and the vehicle’s engine!
Therefore, we need to be extra careful during the research of the correct replacement clutch (electromagnetic clutch, clutch with limiter or coupling). If a clutch with different specifications than the original (diameter, ribs, power consumption, stiffness of the absorbers..) is installed,
we will encounter output problems of the system or, at the worst case scenario, the premature failure of the clutch itself and the compressor.
At this moment KRIOS A/C offers a range of more than 100 compressor clutches readily available in range.
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This article contains information provided by KRIOS AC.
