Climate control: everything workshop professionals need to know

When a customer comes to your workshop with an A/C compressor on the fritz, it’s almost always the peripheral equipment that’s at fault, not the compressor itself. Here’s everything you need to know about replacing the compressor in a nutshell.

The A/C compressor—how it works and what it does

The A/C compressor compresses the gaseous refrigerant, heating it up in the process. In this form, it is fed from the compressor to the condenser at the front of the vehicle and cooled by ambient air and the fan. As it cools, the refrigerant changes back to a liquid state. It then flows through the filter-drier and is cleaned. Any remaining water particles are removed during this process. The evaporator is located in the air duct inside the A/C system. This is where the refrigerant changes its state once again—reverting to a gas. The evaporative cooling produced by this process is directed into the cabin and cools the interior. Finally, the refrigerant gas is returned to the compressor from the evaporator—and the cycle starts all over again.

Compressor failure—why it happens

It’s extremely important to determine the actual cause of the damage. That’s the only way you can completely eliminate the original defect and any further damage. Otherwise, the compressor could fail again.

Negative result in the A/C Performance Test => compressor damage

Typical signs of a damaged or defective A/C compressor:

  • Customer complaints such as “poor cooling performance” or “loud noise when turning on the A/C system”
  • Leaks
  • Error code in the HVAC control unit or engine/central control unit, for example, refrigerant pressure is too low or too high, electrical faults
  • Negative result in the A/C Performance Test with the MAHLE ArcticPRO® ACX A/C service unit

Common causes of failure:

  • Insufficient compressor oil or refrigerant
  • Leaky A/C system
  • Solid matter contamination (e.g., chips)
  • Moisture in the A/C circuit
  • Mechanical defects, such as defective components in the compressor: magnetic clutches, belt pulleys, bearings, pistons
  • Electrical faults
  • Refrigerant loss: condenser damaged by stone chipping
  • Compressor oil contaminated by metallic dust

To avoid problems with the A/C system in the first place, it’s best to service a vehicle’s A/C system every few years. Here too, MAHLE Aftermarket has got your back—with the ArcticPRO® product line.

Click here for an article with video on A/C servicing with the MAHLE ACX:

Article: 'For a great condition'

Replacing the compressor—here’s how it’s done!

Click this link for downloadable instructions on how to replace a compressor. It’s a step-by-step guide that you can print out for your workshop.

step by step guide [PDF; 104 KB]

And click here for our assembly poster and installation instructions—for you to print out and display.

installation poster [PDF; 277 KB]

installation instruction [PDF; 2582 KB]

Or simply watch our installation video, for an A/C compressor replacement done right.



We regularly provide technical tips relating to the powertrain, thermal management, and mechatronics in automobiles.


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