Vehicle air conditioning and heating system providing engine on and off operation

A heating, ventilating and air conditioning (HVAC) system for use in an over-the-road or off road vehicle (102) is provided. The HVAC system may be operated regardless of the operational state of the engine. That is, the HVAC system may be operated to condition the interior compartments (128,130) of the vehicle (102) while the engine is running and while the engine is in a no-idle (off) condition. In general, the HVAC system efficiently shares one or more typical air conditioning components with those already found in the vehicle. In one instance, the HVAC system operates an electrically-driven compressor (106) when a belt-driven compressor (108) is idle. In another case, the HVAC system operates both an electrically-driven compressor (106) and a no-idle condenser (160) when a belt-driven compressor (108) and condenser (110) are idle. In yet another embodiment, the HVAC system shares an evaporator (162) between an engine-driven primary air conditioning circuit (104) and an electrically-driven secondary air conditioning circuit (164).