Hi,

My central air unit is on the 3rd floor. When it's on, the air flow on
the 3rd is tremendous and it becomes cold in a second. At the same
time, the air is barely coming out on the 2nd and the 1st floors. The
ducts are old, but I inspected the parts that are accessible and they
seem to be intact. What could be the problem here and what should I
try next?

Many thanks in advance,

Aaron