Two cans should have been enough to engage the compressor. Whether it was or wasn't, if it has leaked out since the dye was put in, there certainly should be enough dye traces to find the leak. The most difficult would be if you can not run it and the leak is in the evaporator. If you can't find a leak anywhere else, aim your UV light at the vent in darkness and see if you can get the blower to blow past the evaporator. You might can see UV dust coming out if it is dark enough and your black light is powerful enough.