I advise you to do it whenever it is obvious that it needs to be
recharged. I once lived in Virginia and did not use the AC during the cold
winter months. I had to have the AC recharged at the end of winter since
my AC no longer produced cold air. Some of the auto related stores such as
NAPA have special thermometers that clip on to the AC vent.
Jason

-----------------------------------

Just changing the cabin filters will make a huge difference. I do them
at least yearly. But if it's not that, I can't say.

'Curly'

It theoretically should never need to be recharged. In practice, systems
start leaking eventually and do need a recharge, but a 2001 is a little new
for that. I figure at the ten year mark about half of A/C systems have
needed recharge.

If your A/C is getting weak, you can change the cabin filter as Curly
recommends. If it has been changed recently it's time to schedule a checkup
with an A/C professional. In the R-12 days you could do almost everything
yourself, but R-134a is a very diffferent beast. I don't know why, but I had
no trouble recharging R-12 systems and failed miserably the time I tried to
recharge an R-134a system. Worse, regulations have made the overhead very
high for professionals. That means you can expect to part with most of $100
US for a check-up, which involves emptying the system by filtering and
capturing the refrigerant then refilling with the measured amount of R-134a.
A check of the operation, along with fixing or identifying air flow and
control problems completes the job.

To rub salt in the wound, a decade after the ratification of the Montreal
Protocol - which included banning the production and mandating other
controls for R-12 and other CFCs - A NASA/NOAA mission called POLARIS
determined CFCs (in fact, all halogens combined) have only a minor effect on
stratospheric ozone depletion. The main culprit is reactive nitrogen oxides,
formed by sunlight. Isn't that special?

Mike