67 Dart AC out again.

Those flame/torch leak detectors only work for R-12 and that is assuming there is any R-12 left in your system. There may be some charge left but just below the level needed to keep the low pressure cut-off switch from operating. Try removing one of the service fitting caps and depressing the center of the valve if you hear a slight hiss the system still has some R-12 in it. If not it is basically completely empty.

When refrigerant leaks out it will carry some oil out also most of the time. This oil will then attract dirt that will stick to it. Look for an oily accumulation around fittings and you may have found a leak.

Remember, as mentioned above, RV compressor shaft seals will leak a very small amount of refrigerant and over a long time the system will be discharged.