Have you put color dye in your A\C system.
try the (Fluoro lite) fluorescent leak detection tracer dye....just put tracer dye with new R12 freon in to A\C system then use
the fluorescent lite to find the leak.
check evaporator for leaks...just remove the wiper motor & A\C blower motor evaporator is locate under the blower motor.
good lock !