Ever noticed "dust bunnies" accumulating on your return air grill?
That's dust and dirt from inside your home! I know most of us don't want to admit that, but it's true. It accumulates there because all of the air that is moved by your A/C unit must pass through that grill and filter to return back to the air handler. That could be as much as 2000 cubic feet per minute! That's a lot of air! And, possibly, a lot of dirt.
It is very important to clean or replace your air filter frequently to keep your A/C in it's best operating condition. Keeping the grill clear of that dust accumulation will keep the airflow at it's maximum as well as making the grill asthetically pleasing.
You could vacuum it from time to time OR:
Next time you're ready to change or clean your filter, turn the fan on and take a wisk broom or dust mop and brush the louvers of the grill. The dust will be drawn into the dirty filter. Then remove the filter along with all that newly aquired dirt.