Sounds to me like you have a leak somewhere. When these systems get low they will blow warm on drivers side and cold on the other as you have described. Normally you can spot the area of leakage because it leaves an oily residue at the leak. Check to see if the compressor is covered in ac oil, also check the lines and all connections. If you decide to just add more refrigerent it will likely just leak out rather quickly without fixing the leak.
P.S. The high side service port is by the air filter housing if yours is like my 1999 gp. If you are using a single line to charge you always charge through the low side which is the one by the firewall. You only use the high side for reading pressure, not charging.
