Indoor airflow in any air conditioning system is critical. Too much air and the customer suffers lack of dehumidification in cooling. Too little air in cooling may freeze the coil causing damage to both indoor coil and outdoor compressor.
Checking airflow is one of the most important checks. Instruments can measure pressure drop across the coil. If pressure drop tables are available, they indicate the cubic feet of air per minute (cfm) moving through the coil. An inclined manometer or Magnehelic gauge are examples of this type of instrument.
A velometer measures the velocity of the air in feet per minute (fpm). If the area of duct is known, the velometer reading times the area of duct (in square feet) calculates the airflow.
There are also simple mathematical formulas that are needed. All of them require measurements be taken. These measurements require a voltmeter, ammeter, and a good temperature tester.