Though there are many correlations between temperature, airflow and humidity the most important for HERS testing would be target subcooling. If your refrigerant is charged properly but has low airflow along your evaporative coil then your subcooling will be high. This can cause damage to your compressor or even ice up your coil. The HERS performance guidelines require a minimum of 350CFM/per ton airflow or more.
If subcooling is low but there is a restriction on airflow, your subcooling numbers may actually achieve its target. The problem with this scenario is that your system will not operate at its proper cooling BTU capacity.
A correct charge should begin with an initial airflow measurement. Only then may you confidently charge a system. Having said that, there are many different variables involved with airflow and refrigerant charging. If you have questions please do not hesitate to contact us at Rapid Duct Testing for further details and clarification.