@xt
this happens too with my mehran long time ago, i filled gas 8 times, all time pressure remain connstant on pressure test, then mech. suggest me same that shAFt seal is leaked so pressure not droping on test but when compressor runs, due to seal leak, gas goes out, gas only go out when compressor is ON & running
i took car to Bashir autos in tariq road, they opened all parts & checked, fortunately they told it was not shaft seal but a minor crack inside compressor, they opened it & do something "tappi" in 600 from outside, then service & fill gas,
after that it was ok for long time , so they were right
so bashir autos a/c are champions in a/C works, even suzuki 3s dealers suggest them for installing a/c in new non f/f a/c cars so go to them directly without wasting time & money
u will thank me after job, i am sure