baka

With the thermostat and the valve to the heater matrix closed, the coolant gets warm very quickly. Normally, the car gets the engine up to temp as quickly as possible before opening the thermostat or heater matrix valve, as you have noticed. It's not the relatively small amount of coolant that's 'warming up', it's the massive stone cold block of aluminium full of oil. I think you are just bypassing this and opening the heater matrix valve early by setting the AC to 'high'. A up to temp car has a coolant temp around 100 deg C, but you can comfortably warm the cabin with the coolant of a engine that's warming up. I doubt there is a resistive element or that the AC is running as a heat pump. My friends old Cavalier could boil your face off 2 minutes after you started it, it was quite impressive.