if you had one of the last models, it would be R134a and takes approximately 800 grams of gas and about 180 ml of oil throughout the system, the compressor it has (harrisson/delphi V5) is an extremely tough unit and is found in millions of cars - its actually a variable stroke compressor (it doesnt trip off - it reduces volume load to ease up the engine when the A/C is not much required e.g. cabin very cold - it senses this from the suction line pressure).
This compressor has an internal sump and needs oil in it, if you just add some oil to the ports your compressor will be starved of oil and will sieze/break quite soon. You are supposed to put about 100 ml of oil in it and it takes PAG150 oil. The rest of the oil is put into the evaporator/accumulator and lines.
It takes a green GM orifice tube or you can buy a spring loaded one (called variable type) and install it.
Flushing the unit as recommended by GM is done through liquid refrigerant being pumped through the items (this procedure is completely alien to all Pakistani car A/C techs) - OR done by using a flush gun and cleaning solvent like acetone then blowing out the lines and evap with nitrogen or very good quality dry compressed air for about 2 minutes each.
Do not wash anything with petrol - it will create big problems. If your condenser was clogged then best is to replace it - You can also buy delphi A/C line filters and install in the lineset (as recommended by General Motors to keep the system clean after it suffered a blowout)
Due to the design of the compressor (it has a variable metering device) - you cannot charge this system just by looking at the pressure gauges, the compressor will upstroke/destroke to keep the system at max efficiency and minimum load this is why you need to install gas in the system by weight. If you experienced a noisy compressor after the A/C work - the gas charge was severely low and the compressor was trying to keep up with this loss - and if your mechanic bypassed the low pressure switch, the compressor basically would have committed suicide as the low pressure switch keeps it from killing itself when there is severely low charge.
You may have noticed a muffler in the suction line of this system, if that was clogged from debris - trying to clean it makes it worse. Its cleaned with liquid refrigerant pump or just replaced.
old mechanics called this compressor as "machlee wali caprice ka compressor"