Finally, I came back to the air conditioning specialist to do one more leak test and, guess what, we found two leaks! The first one is located one one compressor connection. We disconnect and connect again with care and the leak disappears. But the second leak is more tricky. It’s located on the dryer and it’s due to an insufficient length of the thread, which cause a bad connection. I don’t have a solution yet to fix this problem. I used a “soft” pipe instead of the original rigid one, it was perhaps not a good idea. So I’ll try to convince my pipe specialist to make a rigid pipe by re-using the original connections, but when I first asked this question he told me that he could not do that. I can’t simply reuse the original pipe because it’s damaged (bent).
Because of the leak discovered earlier when testing the circuit, and following the advice of the specialist I saw, I decided to replace all the pipes, hoping to fix the leak and increase the system reliability.
Modern air conditioning pipes are a lot more rigid than the old ones because they are not made with rubber only, they have an inner pipe made of a plastic material like nylon (or something like that). They will be significantly more better, for sure, but having some new pipes made exactly like the old ones doesn’t guarantee a good fit. And connections or fittings are longer and reduce the installation possibilities in limited-space situations, like there are many with a SM. So this installation required numerous adaptations and fixes, regarding the length of pipes and the angle of connections and fittings.