Also there is other HVAC air handling units (840 lb) and air cooled condensing units (860 lb each) will be supported by slab on grade. Will a 6" thick slab on grade be adequate or is there some reference I can use to do the calculation?
860lb is not really something to get excited about. What is the footprint size of these units? I.e. How far are the 4 supports spaced? The 150mm slab on grade should be OK.