Question

weak airflow on forced - air systems at the registers is caused by all of these except
dirty filter
a clogged indoor coil
a slipping fan belt on the fan motor
dirt on the fan blades
low refrigerant charge

Explanation:

A dirty filter restricts air - flow. A clogged indoor coil can impede air movement. A slipping fan belt reduces fan speed and thus air - flow. Dirt on fan blades can affect aerodynamics and reduce air - flow. Low refrigerant charge affects cooling capacity rather than air - flow at registers.

Answer:

E. low refrigerant charge