Adam,

Your SMX panel can do some diagnostics. Do the check and it is likely it will indicate you are low on R22 freon.

It can be charged by any capable refrigeration tech. Insist he charge it according to the pressure charts. As Jack pointed out they are sensitive to under or over charging.

You will know when it is right. The sight glass will not run clear, not will it run foamy. It will show a liquid with bubbles. All condensing units have sight glasses.