AC compressor pick up sensor

my ac compressor clutch comes on for three seconds, then off and flashing ac button light after. I have replaced the compressor with a remsnufactured unit, and it still happens. my mechanic thinks the compressor needs to be disassembled and the "internal" sensor needs replacement. isn't the speed sensor just the black plastic unit that screws onto outside of compressor with one screw? I tested it by connecting 12v positive and negative to outside 2 of three terminals, and measuring 2.4 volts at center teeminal, that goes up to over 9 volts when a magnet is placed near sensor, so I assume it is good. is there even any internal sensor or problem inside the compressor that could cause the flashing ac light on switch? the ac works fine when I have a jumper wire in place of relay, but very inconvenient to remove and reinstall to turn ac on and off. I've ordered a new toyota ac amplifier as it seems like most likely suspect at this time, but not sure how to test it directly without just replacing it. I need to know if I should not take back to mechanic who suggested compressor dissasembly. thanks!

 

There’s a guide here: https://www.tacomaworld.com/threads/a-c-light-blinking-troubleshooting-guide.440200/