There is a pressure temperature chart for each refrigerant such as R-22, R-410A, R-123A and R-134A (which is commonly used in motor vehicles). You can download these charts for free from google and see what should be the refrigerant suction (return coming to compressor) and discharge (supply from compressor) pressures are at a given ambient condition (the temperature of the place where gas is being charged). Icing on lines occurs in case of low refrigerant charge, read car manual for exact gas quantity required in the system. Most of the gauges used by our technicians are meant for R-22 not R-134a hence they never fill gas according to the desired conditions. Try Suzuki, Honda or Toyota authorised dealers they might have the appropriate gauges.
All refrigerant systems should be properly vacuum before charging with gas. Air in the system decreased the air conditioning efficiency and increases the power consumption. How do we check if the system is properly vacuum? The vacuum pump has a discharge line, when the vacuum pump is running it is drawing air from the system, they normally run it for 10 to 15 minutes and then introduce the refrigerant. Where as the discharge line of vacuum pump should be submerged in water so that one can see air bubbles. When the air bubbles stop that means that the system is free of air and now you can add refrigerant. Most mechanics don't have a vacuum pump so what they do is purge, add gas in system from one side to push out air from the other side, this is the most inefficient way.
Lastly, Cultus has no built in cabin air filter which means that the evaporator coil is chocked with dust. The compressor gives optimum efficiency at around 3,000 engine RPM not at low speeds (you can check this on the highway). Similarly, the condenser coil is also clogged with dust, smoke and insects. Add all these and the incompetency of our technicians. And this is not only the case in the motor industry, look at domestic air conditioning market.