Stormin Mormon wrote:

I've seen units which "ran fine" but were in serious
need of professional cleaning. The challenge is to
find a company that does good and honest cleaning.

A few years ago I took the cover off the condenser unit and cleaned it
with a garden hose and a nozzle that gave me a high-velocity spray.
Last year I partially removed the evaporator A frame out of the furnace
plenum and cleaned it with a combination of vacuum cleaner and
high-pressure air.

I also removed a couple of baffle plates that forced all air through the
A frame so that about 1/3 of the plenum opening was free of airflow
restriction and the other 2/3 would have to flow through the A frame.
This took some load off the fan and made the furnace more efficient for
winter heating. I noticed no reduction in the house cooling performance
last summer after doing that. In fact, the extra airflow made just
having the fan running (without A/C on) was probably more sufficient
more of the time.