I am trying to lower the fan speed on blower fan. It is currently set to factory default setting. My AC is 3 ton unit. Model no is 4A7A3036H1000NA. The fan settings on IFC are like TAP 1, 2, 3.... and currently it is set to Tap 7 which is the last setting. But when I look at the chart for CFM vs External Static Pressure Tap 7 comes around 2000 for all the numbers. My question is should I lower the fan speed to get closer to the required CFM instead of letting it be on factory default setting? I know that first static pressure need to be measured but again the factory default setting seems to be high for 3 ton unit.
When I was still doing residential work the normal temperature drop across the Coil was between 15F. and 20F. A temp difference above 20F meant that more air flow was needed and a temp below 15F meant that there was too much air. Unless things have changed recently or you have a special A/C system you can use these temp drops as a guide line. Just buy a temperature thermometer or a probe type and measure the air temp difference across the coil. my 2 cents