A module (11) for a bus rooftop air conditioner is self contained in that it has all the necessary components including a compressor (27), if desired, which when supplied with electrical power, can provide conditioned air to the passenger compartment of a bus. In addition, an electrically powered heater (24) is provided in the air flowstream such that heated air can also be supplied to the passenger compartment when desired. Multiple units provide for incremental capacity requirements to be met as well as limp home capabilities.
