Hello, I request excuses by my bad writing, I am owner of a 87 328 (GTS Turbo), the last month, I put a conditioned air compressor new, I have verified that even loses the gas, where I must look for the loss? Regards. Alfredo.
There are flourescent dyes you can put in the AC gas. Once that's in, use a UV light to search for the leaks. That will tell you where your leak is.
There is an excellent review of the A/C system for a 308/328 series on the "other" ferrari forum web site. Go to the "technical archives" and you'll see the post. www.ferrari-****.com replace the **** with "talk" and you'll find it.