Hello,

With 12v present at pressostat connection means the controller is working well. Could be your clutch coil, gap or grounding wire (if present). Yes you have already tried to bypass the pressostat connection.

With engine OFF check the gap it should be between 0.011 to 0.023 inch. If the gap is more than that adjust the gap (may need to dismantle compressor clutch or take it to ac shop).

With engine OFF also run a wire from positive battery terminal straight to compressor wire (disconnect the ac compressor electrical plug first). The clutch should engage. If its not then the coil is probably toast. Check if there's a grounding wire between ac compressor to engine. Some cars do especially if the compressor is mounted via rubber bushings (same as alternator bushings).

If compressor grounding wire is present try to bypass it with another wire just for testing (along with the positive wire testing above). Try to push the clutch to engage (press on it) to rule out gap problem during this testing.

I don't usually rely on codes for ac works as the testings above are simple. If the car comes with ECC (electronic climate control) type of controller then ac codes might be useful as it uses so many sensors in the system. ECC have AUT (automatic) selector on the ac control panel. If the car comes with MCC (manual climate control) the above testings are just sufficient.

If the clutch coil is toast you need special tools to replace it. Or take it to the ac shop. Some shops may recommend replacing the entire compressor (for ease of work or they don't have the special tool plus no coil spare part). Some may even recommend converting to R134a.

Hope these helps,
Amarin.