The A/C compressor is engaged via a single wire that comes from the 'A/C' button on the dash board. I want the A/C button to disengage when the throttle is at 50%. The throttle position sensor (TPS) works based on voltage. 0.5-4.5V to be exact. 0.5V is idle (0%) and 4.5V is wide open throttle (100%).
What do I need to automatically disengage the A/C switch when the voltage exceeds (for example) 2.5V from the TPS?
The A/C compressor draws a lot of power from the crank and makes acceleration hard in a pinch.
Thank you.
Sorry automotive electronics are mostly very simple systems and this actually exceeds my current understanding of circuits and relays.
Best Answer
on some cars (scion tC) it's simple to remove the climate control unit from the dash. Behind it is a cable with 30 odd wires coming out of it, and a wiring diagram tells us which wire feeds (somewhere else) to (something else, presumably ECU) that handles actual compressor control. Installing a Reed relay in series with the correct wire, and wired "always on unless small comparator circuit triggers" could work. If you need a schematic I could edit one in.
the scion tC ECU is supposed to sense and disengage the AC clutch during heavy acceleration, but that doesn't happen.
Your question has inspired me to do this for myself. It might be good to implement a delay circuit so that the relay doesn't cycle with every shift (if yours is MT like mine). My original thought was to manage cruise control and AC state based on OBD2 data to keep AFR at the engine's preferred 'stoichiometric' 14.7:1, e.g. slower uphill and maybe AC off, faster downhill. At that point, it's not too much extra to add a laser distance detector to sense distance to the car ahead of you to automate cruise, which is what really would be nice.