I suspect the OP is thinking of the battery.
I thought that function was called "Rest"? I had it on my CLS, as you say it simply has an electric pump to circulate warm coolant after the IGN is off and one presses the REST button on the climate control.I have the auxiliary heater function (option code 670), but that only works when the engine is hot, circulating coolant after the engine is switched off to utilise the heat already there, so it's no use from cold. There's nothing else.
Unless somebody knows different...?
The very same; there's nothing else, afaik. It may well be possible to install an aftermarket heating element in the block or lower radiator hose, powered from the mains, but I've found nothing to suggest MB installed anything powered by the car's own electrical system, which is what I meant. I'm not that bothered; if there was something there I'd use it, but warm-up to the point where the demist function is effective is somewhat slower than with the SLK, but not dramatically so, and I can live with it.I thought that function was called "Rest"? I had it on my CLS, as you say it simply has an electric pump to circulate warm coolant after the IGN is off and one presses the REST button on the climate control.
I recall diesel W211 models had an electrically powered (Peltier?) heater in the heater system that came on with the IGN to boost cabin heat until the engine came up to temp.
My S203 had an electric boost heater for the engine block but that only operated if there was a surplus of charge from the alternator. I never noticed any effect...
I'm old enough to remember when heated rear screens were a luxury...