Search this page (below) for "Air Conditioning" topics. mrsha posted two
about problems he had charging the system himself. I posted one titled
"What is correct way to re-charge air conditioning?" that has some good
follow-up.

What has probably happened is the refrigerant has leaked out
so the system won't run. But, as pointed out in one of the above
threads, there is a detaile dprocedure techs use to trouble-shoot.
(But leaking regrigerant is very common.)

If leaking, the systemn needs to be correctly charged and dye added.
The dye helps pinpoint the leak (at some time in the future). If the
leak is small, you may go a long time until another charge is needed.
If the leak is large, it can be very expensive to fix since there is a
lot of labor charges involved. See http://volvospeed.com/Repair/ac.htm
for the nasty details.