drees wrote:Sounds great, but (sorry!) - one known issue is that the heater will come on with the A/C when the system isn't working hard to cool. You can see this typically when ambient temps are 65-75* and the interior of the car has cooled off already. HVAC will register 500-750W or so, but if you drop the temperature a degree you will actually see power draw go down.
I presume that this is done to help dehumidify the air, so humidity levels probably play a role here as well.
It doesn't sound like there's a way to keep the heater from coming on in this situation where you want a small amount of A/C but no extra dehumidification with your mod? Am I missing something?
Yes, I did not see this happen as you say when I had the Leaf fully instrumented. It will sometimes run the A/C for dehumidification when the heat (especially for defog) is on, but I've *never* seen it run the heater when the A/C is called for! I had instrumentation in the car to tell me the current heater PWM values, and I did not see this. I suspect for whatever reason, this is actually just the A/C running at a low idle to keep the system's high side/low side pressures at their optimum balance to ensure the expansion valve is doing the most efficient transfer. Disturbing the temperature may make the system back off for a bit to reset the algorithms. If you can come up with an exact and reproducible set of test parameters, I'll be happy to test it both the PTC duty cycle as well as the compressors and see if I can confirm it. Maybe it's due to our fair Bay Area weather here!
If I am somehow wrong and this turns out to be true, and you simply can't tolerate the heater, the "fix" is to just turn the A/C off for a bit until the delta T is a bit larger and then turn it back on. Or, if you that concerned about the power, you probably don't want anything using extra power!
If you can propose a better way to implement this without needing to drill holes and add switches, I'm all ears!