Air conditioning systems are designed to deliver 400 cubic feet of air per minute (cfms) to provide one ton of cooling capacity. ie: 1 ton = 400 cfms, 2 tons = 800 cfms, 3 tons = 1200 cfms. Most technicians and installers have never measured how much air blower is moving through an evaporator coil or heat exchanger. The evaporator coil exhorbs heat from the air; so with low air flow the system operates at a low pressure, so most technicians will add freon to the system. This causes overcharging of the system, which will cause excessive refrigerant oil return, washing the oil off of the compresser. This will cause premature failure. The best way to check air flow is with a static pressure guage. The results should be compared to the manufactures air performance chart. This will determine how much air is moving through the system. Most equipment manufacture’s systems are designed to handle a .50 static pressure. Static pressure is the resistance the system will handle. The higher the static pressure, the lower the air flow is, thus causing poor equipment efficiency and eventually pressure failure. It is a must to check air flow first and then go from there. Hope this helps..