Dietz says failure to replace the air filter on schedule is one of the most common reasons that an AC unit will stop working. "Homeowners who ignore this basic task, risk at the very least make their unit work harder than necessary just to try and push the cooled air through a clogged filter," he notes.
"In extreme – but not completely uncommon – cases, a unit can be completely incapacitated and have to be replaced because the cool air, having nowhere to go, circulates back into the evaporator coil, causing it to freeze and fail," he adds. The evaporator coil is a network of tubes, filled with a coolant called refrigerant, that remove moisture and heat from the air.
A clogged filter hinders the flow of air through the unit, reducing its efficiency and making it tougher to cool your house. Consumer Reports recommends that filters on central air conditioning units be changed once a month, especially if you have the air conditioning running constantly, or have pets who shed fur.
To make it easier, Dietz says, many of today's advanced thermostats automatically notify homeowners of the need to replace a filter.