If it is a CAT work tool or machine there are updated couplers that allow you to connect the male under presure. The coupler is identified by it's black anodizing instead of the ZincDichromate (Gold color).
Hammers are alwafull no matter the brand because the accumulators seem to constantly apply pressure to the system.
If you always bleed the pressure off using the methods described above, and install the improved coupler you won't have any problems.
If you can ever get one line connected then you can release the pressure back through the work tool using the above described methods.