 Automatic temperature control systems can take the best course of action in regulating the compressor operation, amount of reheating and blower speed depending upon the external air temperature, the internal one and the cabin air temperature value or a rapid defrost effect requested by the user.Because the heater core cools the heated coolant from the engine by transferring its heat to the cabin air, it can also act as an auxiliary radiator for the engine.If the radiator is working improperly, the operator may turn the heat on (together with the cabin blower fan placed on full speed, and with the windows opened) in the passenger cabin, resulting in a certain cooling effect on the overheated engine coolant.