I own a 2-story home with zoned space pack A/C. In my backyard are two condensers, each resting on what appears to be a plastic pad. This system is about 6 years old (I have only lived here 2 years). The condensers are starting to list (lean over), and they look like they've sunk into the ground a bit, to the point where there is a lot of dirt/mud around the base of the units, even though I cleaned them out last spring. My thought is that these condensers should be temporarily removed, and that a concrete slab be installed on top of gravel/sand, and then the condensors be re-installed. One contractor said that they could be mounted on rails (basically L-shaped supports that are anchored to the foundation of my house), which holds them 3-6" above grade. Does this sound like a good choice? Is there an industry standard for how these condensers should be mounted and supported? The current pads are not keeping them level, and are such that too much dirt/mud is getting to them, surely decreasing efficiency, and possibly threatening their usability. Any suggestions for how these SHOULD be configured?