running it without or low gas destroys compressors due to
1 no oil (gas carries the oil too)
2 no internal cooling (the cooled gas suction line from the evaporator cools it)
3 extremely high head pressure
but your car should have a low pressure switch that will not allow the compressor to engage if its low on gas, (most mechanics short the wiring and weld it closed) due to the owner or the A/C mechanic of the car being a cheap dumb idiot - as he cannot afford to spend another Rs500 on the switch but will happily fry his Rs10000 compressor