the compressor found in santro is amazingly heavy duty, its also found in some nissans and mazda, Finding it as replacement is easy too.
Most mechanics in pk dont know how to fill oil in it and then proceed to destroy it. The factory oil charge in it is single capped PAG46 oil which will absorb moisture very quickly. You can flush all oil out and fill with double end capped PAG46 oil (you should do a full flush anyway if you are replacing the compressor)
Its vital to use a vacuum pump to pull the air out before filling with refrigerant. It also has a requirement of first letting the liquid refrigerant push itself into an empty system from the hi side port with engine off till the pressure stabilizes (usually this pushes about 300 grams into the system) - the rest 200 grams is then sucked from the low side port.
The high side line is then disconnected and flushed back into the low side port from the manifold to make sure all the charge is correctly put in.
Its a very simple and basic procedure. The toyota duet compressor is a piece of trash old school technology useless item - the only reason its being installed in pk is because the illiterate and moronic mechanics dont know how to work on A/C units.