Inspecting AC system on vehicle before summer months

I owned my Honda Accord for over 12 years. 3 of these years, I was
caught off guard when my AC
system was less than adequate when the summer months hit. The best
example was when I was driving to Las Vegas
in 116 degree weather and discovered the hard way that my AC was'nt
up to the job. One year it was a problem with the
evaporator, the two other years it just needed a refrigerant refil.
I would like to prevent these suddent discoveries in the future.
Before the summer months hit, I will ask my mechanic
to inspect the AC system. Should this be done every year? Can this
be done when the weather is still cooler? What
specifically should I have my mechanic check. How many hours of
labor should this cost me?
Thanks