It would be a big job getting to that condesate pan. If the pan is overflowing then it's likely that there's a bit of gunk in there that's clogging the drain port or the pvc piping is clogged up. An easy fix would be to remove the pvc pipe and suck on the pan drain port to clear it. I know it sounds yucko but it'll do the trick. You should also pour a water/bleach mixture down the pvc piping to clean it out before reattaching it to the drain pan.
Most times the drain piping is just a clear flexible hose so if you can't detach the pvc piping then you may need to cut it and reglue it in order to clean it out.
Also, make sure you change your filters often, this helps in preventing the clogging. Below is a link that'll help you out.
http://www.rd.com/content/openConten...ontentId=18069