Strange question I know but, Does anyone know for certainty the source of cabin heating? I’m not asking for “l think”, or “l assume” responses, but a response from someone who knows. The reason for the question is related to my charging system. Being of the generation where car heat came from an antifreeze radiator, and air con was the result of a hand crank window, I’m curious if the auto world (and in particular, the 2018 971 P4) now use reverse cycle AC, or electrical resistance bars, or combination, as the source of cabin heating. I’ve discounted the possibility of engine heat given the distinct lack of a motor oil tang in the air when the heat is on. After all, Taycans need heat in the winter so Porsche’s come up with something.

In very cold (less than 30 degrees F) weather the voltage gauge consistently reads 15.1 to 15.4 volts. This is a constant 15.x volts. I can go from my house in MA and drive 80 miles into NH on highway and back road and voltage stays in the fifteen range. I can stop, shut the car off, wait and hour or more, jump back in car and return home with no change. My Fluke meter says the 15 volt levels on the car gauge are accurate. The next day if the temps go up to say 40, car charges perfect, initially 14ish then dropping to 12-13. The service department has looked at this a couple times and last year at this time found a defective part in the battery management system. That seemed to fix it. But with the onset of winter 2021, it’s back.

I had a conversation recently about autonomous and electric cars, and one of the folks made the point that automakers have been working on this for a long time in the background by converting vehicle sub systems to self contained electric systems, I.e. power steering, oil coolant pumps etc. That triggered the thought that my charging issue might not be a supply issue, but consumption. Where my issue is only in cold weather, could this be related to the heating cycle?