Using a 2000 4runner FSM while trying to diagnose DTC P0505, it says if you pass the idle test, to move on to step 6: Check A/C signal circuit (See page AC−91).
you can jump the 2 pin AC pressure sensor connector under the hood on the AC line, if everything is working the AC clutch should engage, that should tell you if its a pressure issue and if the AC clutch is working correctly.