Guillaume:
You should try changing your Work Environment.
1. Open the Work Environment and select and apply the
MEP Profile Work Environment Profile
2. If the MEP Profile is not there then go to Command Layout Schemes > Menus and add
MEP Routing (this is the palette you are missing) and the other MEP commands to your menus.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David