chortle wrote:Let me have that same system for the heater, run for a few minutes, off for a few minutes.
Just build a small dial resister and switch with a 555 timer into the power circuit.
Is it that easy or am I missing a whole bunch of important stuff?
Yes, that would work if that is what you want. You can connect the output of the NE555 directly to the gate of the MOSFET.
I'm not sure if it will actually save you a lot of energy because the PTC heaters in the Leaf heat up water to around 160F. So as we all know, it takes a while until you will get usable heat in the interior. During the off periods the water cools down again, so on the next on-cycle you need to put in more energy than if it would have been running continuously.
BTW have you seen the picture I took of the hot water pipes in the engine compartment? The insulation is a joke with parts of it completely exposed. It really dates back to the ICE age where heat can be wasted.
When I find the time I will add some more insulation. That should improve the efficiency of the heating system. It should also improve the effectiveness of your idea.