Click here to download the .pdf version of this blog with diagrams.

CFM is critical to achieve prior to ever checking refrigerant pressures!!!!

A manometer can be used to identify the airflow of an air conditioning system.

Using the manometer, insert a hose into the return air after the filter. With the blower running on cooling speed the reading will be a negative number like -.2” Water Column.

Next, insert a lead between the outlet of the furnace and the evaporator coil.
This reading may be something like .3” Water Column.

Add the 2 whole numbers together to get an External static pressure of .5” WC.

Some manometers have 2 ports which when both are installed as described, will do the math for you as seen in the illustration below. Click here to download the .pdf version of this blog with diagrams.

You can use this information and the blower Data chart in the Install instructions to see what CFM is being delivered.