An air conditioning unit is provided for a parked truck/boat to cool the sleeping cabin. The cabin air conditioner having a cooling unit comprising a cooling chamber with at least one insulated wall having on opposite sides there of a heat sink and a cooling block having there between thermoelectric chip(s) or a high efficient D.C. compressor or cold storage phase change material. The air conditioning unit also comprises an air intake conduit, a cool air conduit, an exhaust conduit and means of supplying power to the cooling unit. A method for cooling the. sleeping cabin through the use of the air conditioning unit disclosed in the invention is also provided.