Every time we press the AC switch to turn on the air conditioning, we hear a "pop" sound from the engine. Some cars can still hear it after using it for a period of time, and we can hear it multiple times, while others can only hear it once. What's going on? Is it normal? The sound can be heard, indicating that the compressor of the car is equipped with an electromagnetic clutch. The "snap" sound is the sound of the electromagnetic clutch being engaged, which is normal. But it does not mean that the compressor is fixed displacement. Some variable displacement compressors also have electromagnetic clutches, and there is also a noise during operation. Next, let's talk about how the compressor works? Why do some cars not make this noise?

When the air conditioning is not turned on, the pulley of the compressor keeps rotating, but it is only idling, and the pulley is not connected to the compressor shaft. When the air conditioner is turned on, the electromagnetic clutch is energized to generate suction, causing the drive plate and pulley of the compressor to tightly fit together. At this time, the pulley can drive the main shaft of the compressor to rotate, and the compressor starts working. We can hear a "snap" sound, which is the sound of the drive plate and pulley engaging, and it can also be considered that the sound of the compressor starting to work is normal. Some cars do not have this sound because the compressor in the car does not have an electromagnetic clutch, so naturally there is no such sound. Compressors without sound are generally inclined plate type and variable displacement compressors.

Even with an electromagnetic clutch, some cars often hear the sound of suction, indicating that the compressor has a fixed displacement. The amount of refrigerant compressed by the compressor is constant each time. If the pressure of the air conditioning system is too high or the temperature of the evaporator is too low, the electromagnetic clutch will disconnect. When the pressure decreases or the temperature of the evaporator box rises, the electromagnetic clutch will resume operation and you can hear another "pop" sound. A fixed displacement compressor has this characteristic, either working or shutting down, only these two states, so during the driving process, you will repeatedly hear a "bang" sound. However, although the machine was shut down, the cooling was not affected and the air blowing out was still cool. Because the temperature of the evaporator box is already very low, the machine stopped, and when the temperature of the evaporator box is high, it will continue to work.

The variable displacement compressor can only hear one sound at the moment of pressing AC, and then it will not be heard again because it will not stop and the electromagnetic clutch is always in the engaged state. It controls the cooling capacity by changing the displacement of the compressor, rather than shutting it down. If the temperature is too low, it will shorten the stroke of the piston, reducing the amount of refrigeration required for each compression. As a result, the load on the compressor will be reduced, the refrigeration capacity will be reduced, and the temperature will not be too low. If the outlet temperature is too high, it will increase the amount of refrigerant, which is adjusted by adjusting the amount of refrigerant compressed each time to adjust the temperature. This is similar to the frequency conversion of household air conditioners, and it will also be more fuel-efficient when used in cars.

From: WONDEE Autoparts

2024-4-18