Originally Posted by tn7con

In response to papatrick, the IC 741 op amp can take supply voltage as low as +4.5v DC (typical supply voltage for the 741 op amp is 4.5v to 18v). The datasheet *recommends* minimum +10v DC for the most stable drift free for most temperature range, it doesn't mean that it must take minimum +10v as the minimum. Reference here or here.

Originally Posted by papatrick

Thank you all for the info. I just refined this procedure slightly.
-I did not buy the Techstream device.
-I did not use any software.
-Also, my wiring colors are different since I have a Sienna 2011.
-The AC mechanic just told me that my system did not have any leaks, and he was able to force the clutch/compressor ON, but did not understand why it was stopping shortly, the AC was not working.
-After searching for similar behavior on the WEB, I concluded that it may be the problem described here.
-Rather than cutting or stripping wires, when I had the controller in my hand, I decided to unclip and simply remove the cover to access the connector pins inside the controller.
-After removing the cover and identifying the pins based on the pictures of the plug F50 provided here, I simply put the multi-meter on the identified pins and turned the car switch at ON while everything was plugged back, to measure the voltage.
-3.67 V, it confirmed that it was my problem also.
-Then, I identified a pin with 12 VDC, the first one on the left. It is better to respect the spec sheet of my ampli op, minimum supply voltage ±10 VDC. 5 VDC not enough.
-I then unplugged the controller, cut the flow sensor pin at half its lenght, to be able to solder a wire on each side for the input and output of the ampli op circuit.
-I used the 12 VDC supply for the ampli op, and a 500 Kohm 10 turn potentiometer adjusted to 10% of its extremity to give a slight boost.
-After soldering everything, I went back and installed the controller and turned the car switch ON and measured the new voltage, and adjusted the pot exactly to reach 4 VDC.
-Put back the cover, re-installed everything.

Air conditioning perfect again!