Clogged AC, what pipe should I clear out?

Sorry if this is the wrong place but I'm at witts end here. After taking a shopvac to the various PVC pipes by the AC units in hopes of sucking out a clog (thinking it may be insulation). That didn't work and it seems the other typical resolution is to pour bleach/draino down into the AC unit to clear it out... Problem is there's three different options I have. Any suggestions?

http://imgur.com/a/5htMo