To the OP, when I was doing AC for the first time on my Guardian, I did it at level 35, because I just really wanted one trait first.
This is my build:
http://gw2skills.net...Ef4EhtgqCx7qgCB
The Mace and Shield set is to be able to camp right in the face of your boss and negate damage through blocks. The amount of blocks, protection, etc you get help you get off 2 or so healing strikes with your mace. When everything 'defensive' is on CD, switch to Sword and Focus and spam the 2, 4 and F1 skill for a chain blindness and burning. Every time you block, you burn the enemy (which is a big part of your damage, so if you can, get condition damage on your gear. Now burn doesn't stack, but you'll be happy anyway to get as much burning on the boss (duration) as possible, since you'll have to kite in AC regardless of such a 'tanky' set-up. (Full out tanking will get you killed) So just dodging back at times, regroup with your ranged attackers, throwing up a wall of reflection and taking a deep breath and let CDs come up is necessary for your survival anyway. It's good then, that you're still doing something because of the stacked burns on the boss.
With this build, I managed to only die to the twins, and that's only because it's the first dungeon and people are not really aware that you need to seperate them. So keep in mind that you'll have to be sacrificial and try to lure away the boss that your team is not attacking. I actually managed to kite/Aegis-tank/blind one of the two bosses almost long enough for my other 4 team mates to finish the other boss off.
Anyway, it's a good build, and really works well at tanking, but it's not a forgiving build. You can die fast since except for the number 3 skill of your sword, you're really not doing anything from range. So you'll constantly be in the melee range of everything, drawing fire. Mistiming a F3, Mace3 or Focus5 will kill you.