get a cheap gauge, see how much is in it.
it's probably low.
sometimes you can top them off and they're good for a long time.
if it's leaking/loosing refrigerant, replace the orings at the comrpessor, schrader valves and hoses that go to the A/C compressor and that fixes most problems. what I wrote above is for an 01-04 H6 engine and will be different but the principles and locations of the parts are the same.