Most likely place to leak the dual air conditioning syst. on a Eagle modified on 1993 Dodge Ram Van B250

Five times serviced the A/C, within a month is empty.Ink used to locate leak does not detect leak. The van is an Eagle, with dual system. my eMail: I will appreciate any sugestions. Than you.

Asked by for the 1993 Dodge Ram Van B250
I would use a leak detection dye that will show up with a black light with the next A/C re-fill. Then when the system becomes empty, there will be a die trace that a black light can see, but it still may be tough to locate, for example it may be inside the dash etc.
Thak you for sugestion; but, this action has been repeated five times!