A mounting assembly for mounting a wall mounted air conditioner (AC) unit on a railway instrument house is provided. The mounting assembly may include a house wall including an outer metal shell layer, a middle insulation layer and an inner plywood layer. The mounting assembly may further include a threaded part coupled to the outer metal shell layer. The threaded part is configured to receive an AC mounting hardware of the wall mounted air conditioner (AC) unit to secure the wall mounted air conditioner (AC) unit to the house wall such that the threaded part enables the wall mounted air conditioner (AC) unit to be installed or removed from outside of the railway instrument house. The mounting assembly may further include an AC unit cage for protecting the wall mounted air conditioner (AC) unit. The AC unit cage has at least two side doors and a front door such that each side door of the at least two side doors is locked within the front door by corresponding bolts or a quick lock. The AC unit cage is configured for mounting on the house wall.