1- Never bypass the ac pressure sensor. It's there to protect against compressor self destruction once damage occurs and/or a leak releases refrigerant. A sealed system uses refrigerant to move lubricating oil. Loss of refrigerant means less and less lube returning to the compressor. Bypassing a pressure sensor simply allows compressor destruction from lack of correct refrigerant.
2- When a compressor is replaced, it's recommended to replace the receiver/drier to ensure removing any minute moisture in a system after repairs. Oil must be added in the same amount that was in the compressor.
3- New flat seals and O-rings used where fittings are separated. R134a O-rings are lubed with pag oil. Some flat seals do not require lube.
4- Once a repair is made, an electric vacuum pump is used along with gauges to remove all air and moisture, for at least 30 minutes. After monitoring both gauges with zero needle movement, especially the low side gauge, shut off all valves and vacuum pump. Monitor both gauges for needle creep, implying a leak exists from incorrect repairs, poor/corroded fitting surfaces not sealing perfectly, other parts with damage, poorly maintained gauge fittings and hoses. Once a vacuum holds without needle creep for 15 minutes, a repair can be considered fine. Inject one can with engine off, then startup and inject whatever amount is needed. Blower set on medium-high, floor/face vents selected. If you get this far, you should have restored ac back to factory condition.
Vehicle ac repairs are not diy friendly and require advanced knowledge of refrigeration, diagnoses, troubleshooting, repair and proper use of equipment.