on my 300SE/126, there are 2 AC drain lines. Located on both sides of the heater box. Looking up from underneath the car you do not see a hose. Only a small rubber opening, or sometimes a rubber spout looking gizmo. The left drain which I recently replaced, opens in an angle towards the Transmission, rather than straight down which makes it more difficult to locate. I assume (never assume) the right side is the same.
They are in the general vicinity of the front seats, so seeing water collect on the Garage floor sounds right. If however the water is collecting in the car itself, this most likely indicates a collapsed drain hose that should be replaced. The OE drains are lovely pieces of over-engineered rubber,coil spring and foam. A simple rubber hose replacement will do fine and cost a fraction of the cost.