VemsAudiAan mot55/pin41 A/C idle up => voltage divider to protect mch3 (raw extra ADC mcp3208/3 ).
We assumed it is 5V or "12V", and 0V when off.
The mch3 has an 1 + 100k / 75k voltage divider (from EGT2 ad597 output), so
68k series with the 100k (in heatshrink coming from mot55/pin41) makes the voltage dividor ratio:
- 1 + 168k / 75k
- Vdiv=1+168/75 ( = 3.24 )
- V=[5, 12, 16]
- V ./ div = 1.54 3.70 4.94
So dividing 5, 12 and 16V to => 1.54V, 3.7V and 4.94V respectively (activation threshold is normally around 0.9 .. 1V). So it should clearly detect on and off condition. (and apparently it does, A/C idle up function became popular).
Please edit:
What raw voltage do you see in view gauges / raw ADC ( mch3 ) when A/C clutch is on and off ?
mswanson: going from memory on my workbench, I had 3.3v when active, and 0v when inactive. this worked with an 'inverted' control strategy on the activation channel in the 1.2.38 firmware settings for idle control AC activation. when measuring the voltage on the car the pin seems to put out somewhere around 10v as opposed to operating voltage of 12-14v. I think this voltage is actually coming from the a/c control head, so its probably regulated down for some reason in the OEM application.