Must all indoor duct registers and inside doors be open to avoid airflow restrictions while charging freon?

The belief that all indoor duct registers and inside doors must be open when charging freon is rooted in the need for proper airflow within the system. When charging a refrigeration system, it's essential to maintain consistent airflow to ensure the refrigerant circulates effectively and that the system can reach its designed pressures. If registers are closed, it can lead to increased resistance within the system, preventing the refrigerant from moving freely and potentially causing incorrect pressure readings or inefficient charging.

This practice is particularly crucial when dealing with split systems or other systems where airflow plays a critical role in the performance and efficiency of the unit. An unobstructed airflow allows for accurate measurements and helps avoid potential issues like refrigerant pooling or improper saturation levels within the coils.

In contrast, the other choices suggest scenarios where either some registers do not need to be open or only specific conditions warrant an open system. These options fail to recognize that maintaining all registers open during the charging process provides the necessary environment for the unit to operate effectively and safely.