A support for mounting an air conditioner for operative disposition in a window, while being free of any supports external to the window and of any metallic fastener contact with the window, includes elongated top and bottom members of lightweight construction, sized and shaped to extend parallel to an interior window sill of the window, with opposite ends of the top member extending beyond vertical side jambs of the window. First and second transverse members of polymeric molded construction extend between the top and bottom members to define a receptacle sized and shaped to slidably receive the air conditioner therein and to interferingly engage an elongated flange extending along an upper surface of the air conditioner. The top and/or bottom members include hand-holds and the top member is adjustable to accommodate windows of various sizes.