Why does my a/c not hold a charge? How can I further solve my problem?

If it is loosing charge, then there's got to be a leak somewhere. I would use a dye to detect leaks, also check drain tube of your evaporator while using a black light. Your leak might be inside the HVAC housing reason its hard to find, if leaking could mix up with water and drain out in the hvac drain tube. A reputable auto repair shop should get you on the right track.

Good answere RAH. Look at the rubber portions of the freon lines first, though. If they are oily for no reason, freon has broken down the rubber. Leak is SLOW but constant. Wrong oil was used, perhapse.

I had the same problem and come to find out it was the high and low pressure fittings leaking. I replaced these two fittings and vacuumed out the system and it held at minus 30 . Added freon and been cool ever since!