A/C system leak

A/C suddenly stopped blowing cold. (Note: all A/C system installed new 3 years ago) Put 24 oz of 134A in using gauged apparatus. Showed 150 psi high side, 25 psi low side. Checked for leaks using black light flashlight, none seen. Began drive to town to replace used 134A. Noticed A/C blowing hot immediately. Upon return to shop checked pressures. No pressure shown, and low pressure switch had compressor clutch disengaged. Went back to town and bought 134a with leak stop. Put almost all of the 22 oz can in, when green zone was acquired, we noticed that every time we functioned the pull trigger the pressure was decreasing.
Rear A/C was not involved in replacement of A/C components 3 years ago.

So I am presuming that is where this very large leak is.