If i had to install ac in Mehran few things I would have done.
1 - Try to install Mitsubhishi scroll type compressor comes in Mini pajero not only better cooling than sandens and all but engine load near to ZERO. Reason why mehran's ac fails is bcoz as the engine gets old it heats up with a/c load.
2 - Install Multiflow condensor.
3- Install a/c compressor on the place of generator and move generator to compressor place.
4- Try to fit a small fan infront of condensor or try to install a powerful radiator fan just like the one that comes factory fitted in new model Alto.