I would recommend reclaiming whatever refrigerant is in there and recharging to specs by weight. If the system still shows a warm left-side vent (and the problem isn't the heater), there is a restriction in the system.

It might be good to note that it is very bad to run your compressor with insufficient refrigerant flow, be it due to refrigerant level or a restriction. Refrigerant flow in the evaporator is necessary to return oil to the compressor. Insufficient flow causes insufficient oil, and eventual compressor damage.