The Insight uses a conventional air conditioning system with a compressor driven off a belt from the gas engine crank pully. This means that the engine must be running when the air conditioning is on. Owners who are accustomed to their hybrid’s gas engine shutting off when they come to stop signs are sometimes concerned when it continues to run when their air conditioning or defroster is on. However, this is completely normal, and necessary for the AC to work. The 2004-2005 Prius, and the 2006 Highlander Hybrid, use an electrically driven compressor, so the IC engine does not need to be on for the AC to work—at least, in theory. Many of our customers report the IC engine will stay running when the AC is on. There is some talk of using a CO2, pressurized to 2500 PSI, as an environmentally friendly refrigerant in the future.