Why is it necessary to evacuate the system before adding freon?

Evacuating the system before adding freon is essential primarily to remove contaminants and moisture. When a refrigeration or air conditioning system operates, it can accumulate various impurities, such as dirt, oils, and moisture from the air. If these contaminants are present in the system when the refrigerant is added, they can lead to various issues, including reduced cooling efficiency, corrosion, and potential system failure.

Moisture, in particular, can react with refrigerants and cause the formation of acids or ice, which can damage components like the compressor and expansion valves. The evacuation process creates a vacuum, effectively eliminating these unwanted substances and ensuring that the system is clean and ready for the introduction of the new refrigerant. This step is critical for ensuring optimal performance and longevity of the cabin atmosphere control system.