In my 2017 Toyota 4Runner I'm interested in a solution to keep recirculation on by pushing a button even when the defrosters are on. In other words, a wire to override the defrosters so recirculation can be on in any mode. I thought about closing the diverter and disconnecting power to that air inlet servo however I prefer an electrical solution instead of a mechanical one. The A/C amplifier seems to use communication signals to the ECU via the CANbus system which may complicate the solution. From youtube I heard you can hold the recirculation button down for 5 seconds to keep it on however this has to be done everytime I turn on/off the car plus won't work when defrosters are on. I added a couple pics of the air inlet servo. Again I want recirculation on at all times; no "fresh air" or "outside air." Please let me know if you have any questions.
Here's a couple websites to help.