That white wire is from the PCM to turn on or off the AC clutch if a bad pressure condition is sensed by the AC clutch cycling pressure switch. If the pressure is too high you've got something wrong in the system that must be fixed, too much freon, clogged evap, something... If the pressure checks out OK (not too high, not too low) then maybe bad is the PCM, wiring, pressure switch, AC module, could be lots of things.