It would help if you could explain how 'A/C failed'. Do you mean it does not work at all or does it work intermittently?
If it is the 1st, then the 'pressure sensor valve' is most likely the pressure switch that turns the compressor clutch on/off.
1. Find the compressor (at about 7 o'clock position to engine fan).
2. Locate the pulley for the compressor. There should be 2 wires coming out from behind the pulley.
3. Trace this wire to the clutch cycling pressure switch.
If this switch is damaged, then your clutch will not engage > no compressor engagement > no A/C.