Abstract: An improved device for mounting and support of window air conditioning units is disclosed along with a method of installation. The device consists of two support assemblies, one located directly beneath, and another, directly above, an air conditioning unit. The lower support assembly also has additional legs that bear on the external window sill, thus providing additional load bearing capacity for the lower assembly. Each of the assemblies is anchored to the interior side of the window frame via tabs located at the ends of each assembly, and secured with self-tapping screws. Two or more vertical rod assemblies anchor the lower and upper support assemblies to each other, and provide additional support to keep the air conditioning unit from pivoting and falling out of the window, as well as serving to resist loosening due to vibration encountered during operation of the air conditioner.