1. It refers to the whole system compressor, condensers/fan, dryer/receiver, evaporator, expansion valve, thermostat, hoses, etc.

2. Denso, Calsonic, Sanden, Mit Air, etc. are branded names. Parang din gamot yan may branded at generic. Mayroon din na Mark IV, Abacus, etc. w/c imo can be called generics na install ng mga aircon shops. Or it could be a combination of compressor na Denso, Evaporator ng Calsonic, etc.

3. Sa pagkaalam ko sa casa lang mayrun brand new Calsonic (correct me guys if I'm)wrong) aircon parts.

4.No idea on this. But it does add considerable load to the engine. More load, more gas consumption.

5. May mga specific model ang compressor, evaporator, condenser and fan/s for certain kind of cars, vans, suvs, auvs and buses. Computed po ang laki o liit ng mga components ng aircon as against the vehicle to which it is installed.