No the one down to the left of the crsnkshaft is definitly mechanical, to loosen it you would loosen the center bolt, and the long stud underneath. The one for the a/c would be the automatic one, if you have loosened a long stud on this one than it too is mechanical. An automatic tensioner is a singal piece unit, which mounts to the block and is spring loaded, The pressure of the spring keeps the belt taught at all times, to relieve the tension, a long bar with the correct socket has to be used as leverage; this is where the serp belt tool comes in.
Take a pic when you can, and i'll know for sure, but from what it sounds like, you most likely have the mechanical version. The loosening nut is uually on the opposite side of the idling pully. Another quick tip, when you get the belts back on, to tension them correctly so they won't slip and sqeal, tighten the long studs in until you can't twist the longest prtion of the belt more than 45 degrees. So, for example, if your tightening the a/c belt; the longest portion is between the crank pulley and the compressor. You would find the center (which is right above the alternator pully, and twist it aas though your trying to see the ribbed side of the belt. When properly tightned, you shouldn't be able to twist it completely around orit's too loose, the most it should twist is about the 40 degrees. This is a good rule of thumb to know on checking all belt adjustments, including sutomatic tensioner style.