Abstract: An air conditioner for being mounted to the wall of an enclosure box is disclosed, the air conditioner having a cabinet, a refrigeration chassis mounted in the cabinet and having a L-shaped frame attached to and dividing the cabinet into first and second chambers with a compressor and condenser in the first chamber and an evaporator in the second chamber, the cabinet has a condenser fan ducted into a screen covered exhaust plenum at the top of the cabinet and the second chamber has a fan for blowing cold air from the evaporator coil into the enclosure, an inlet plenum in the back of the cabinet is provided for drawing hot air from the enclosure and there is a filter holder on the cabinet for holding a filter of twice the area of a condenser air inlet with a filter being turnable end for end in the holder for being used twice.