the A/C compressor is controlled by the ECU - it switches off if you press the accelerator to quick, it also shuts off when the engine starts to overheat, it also shuts off if compressor rpm mismatch is detected (most common case in Pakistan), and it also shuts off if the evaporator temperature is too low or the low pressure switch detects too low gas charge or the high pressure switch detects overpressure.
I would recommend you check the compressor clutch air gap and the clutch face itself, if its deeply grooved get a new one. But first try to adjust the air gap, remove it and move shims from back of the plate to the front to narrow the gap. Check the belt for wear - if the ribs of the belt have sharp edges on the little peaks - the belt is bad. replace it.
Clean the pulleys with brake cleaner to ensure the new belt does not slip.