Airflow issues are all too common in residential systems. I see many systems that don’t function well because of poorly sized, leaking, or missing ductwork, or restrictions and blockages in the air circulation system.
Airflow problems aren’t difficult to spot. For example, with the unit running and the blower door removed, try to put the blower door back on. If the unit “snatches” the blower door out of your hands, that’s a good sign that there’s not enough air moving across the coil or heat exchanger.
Another easy way to check airflow is to measure the amp draw on the fan motor. With centrifugal blowers the amp draw will be in proportion to the amount of airflow the fan is trying to move. You’ll need a good amp meter with clamp-on leads that allow you to take your reading from outside the cabinet with the blower door on. Note that this won’t work on systems equipped with electronically commutated motors (ECMs), as those motors ramp up and down to help overcome system airflow issues. But overcoming an issue isn’t the same as finding and fixing an issue.
We really need to perform thorough investigations of systems on our service and maintenance calls. I know we’re on the clock, and I know there’s a temptation to say, “OK, there’s not enough airflow, I’ll just kick the fan up to a higher speed.” The problem with that line of thinking is that airflow issues cause additional wear and tear on all of the system’s components, and can lead to uneven expansion and contraction of the heat exchanger, which can lead to cracks.
Check the manufacturer’s fan curve charts and know what the system’s airflow should be, and let’s not forget about taking static pressure readings. If your readings don’t match, check for obstructions, such as kinks in the system’s flex duct, dirty filters, plugged secondary heat exchangers, and dirty A-coils.
Finally, never bypass any safeties. They’re there for a reason. Be thorough and don’t take any shortcuts.
Jevaris Pettis is owner and operator of J L P’s Heating Cooling and Major Appliance Repair in Springfield, IL, and program director at Midwest Technical Institute, also located in Springfield, IL. He can be reached at firstname.lastname@example.org