Car A/C Compressor Pulley System Explained

The air conditioning (A/C) compressor in a car is a vital part of the cooling system. It is typically driven by a belt from the engine's crankshaft. This drive system involves one or more pulleys.

How the A/C Compressor Pulley Works

The A/C compressor has a pulley attached to its front. The engine's serpentine belt wraps around this pulley, causing it to spin whenever the engine is running. However, the compressor itself doesn't run all the time. The compressor is engaged and disengaged via an electromagnetic clutch located within or behind this pulley.

• When the A/C is turned on, the clutch is energized, locking the pulley to the compressor shaft. This causes the shaft and the internal compressor pump to rotate, compressing the refrigerant.
• When the A/C is turned off, the clutch is de-energized. The pulley continues to spin freely on the compressor shaft, but the shaft and pump remain stationary.

Therefore, the pulley that the engine belt drives on the front of the A/C compressor always rotates whenever the engine is running, regardless of whether the A/C system is actively cooling.

Analyzing the Options

Let's look at the provided options in the context of a car's A/C compressor drive:

• Rotary pulley: This is not a standard term typically used to describe a pulley in a car's A/C system drive.
• Driver pulley: This term usually refers to the pulley that originates the drive, like the crankshaft pulley. While the engine pulley drives the A/C compressor pulley, the question asks about a pulley *of the A/C compressor*.
• Jockey pulley: While sometimes "jockey pulley" or "idler pulley" can refer to belt tensioners or redirect pulleys, in the context of this question and based on the options, "Jockey pulley" is used here to refer to the main pulley on the A/C compressor itself that is driven by the engine belt. This pulley always spins when the engine is running.
• Idler pulley: Idler pulleys are generally used to route the belt or provide tension. They do rotate with the engine, but the question asks specifically about a pulley *of the A/C compressor*. While the main compressor pulley acts as an idler relative to the compressor shaft when the clutch is off, the term "Idler pulley" usually refers to separate components for belt management, not the main drive pulley on an accessory like the A/C compressor.

Based on the mechanism described, the pulley directly attached to the A/C compressor housing that is driven by the engine belt is the one that always rotates with the engine. In the context of the given options, "Jockey pulley" is used to refer to this specific pulley on the A/C compressor.

Therefore, the pulley of a car A/C compressor that always rotates with the engine, whether the air conditioner is on or off, is the main pulley driven by the engine belt, which is referred to as the "Jockey pulley" in this question.

Revision Table: Car A/C Pulley Components

Additional Information: Belt Systems

Modern cars typically use a single serpentine belt to drive multiple accessories, including the A/C compressor, alternator, power steering pump, and water pump. This belt runs over various pulleys, including the crankshaft pulley (driver), the accessory pulleys, and one or more idler or tensioner pulleys. The pulley on the A/C compressor is one of the key accessory pulleys in this system.