basuu, I have found Pakistan Car AC folks to be technically sound. They charge higher, but they are good. I would probably visit them today as well, as I want them to check my car's AC. It chills good when it is in speed. On idle and at low speeds, it doesn't. And there's too much load on the engine.
The AC system's service will improve cooling and increase the chilled air's throw/blow. In our environment, I believe we should have the system serviced once a year, or in max 2 years.
Here's a simple test to see if you need service: Turn the AC on, and stick a thermometer in your AC vent. Keep it there for 20/30 seconds. Take it out and check if it is zero or lower. If that's the case, then the compressor and gas are fine, and you may need servicing. If it's not that low then you either need a gas change/recharge, or checkup of the rest of the system (compressor, condenser, filter).