The slab of a packaged air conditioner at grade level should be located:

The best practice for installing a packaged air conditioner at grade level is to place it isolated from the structure in order to minimize noise transmission. This is important because packaged units can generate a considerable amount of operational noise due to the compressor and fan. By isolating the unit from the structure, you help reduce the transmission of vibrations and sound into the building, creating a more comfortable environment for occupants.

Isolating the unit not only enhances comfort by limiting disturbances but also helps in maintaining ideal performance and longevity of the equipment, as it reduces the stress on the mounting surfaces and the structure itself. This practice is particularly important in residential or commercial settings where noise control is a priority.