I don't know which model you have but yellow lines are usually for the vacuum door locks. The source lines for A/C are usually green.

If the problem with your A/C is a lack of source vacuum, separate out and plug all the other systems till you have it working and then work each other system similarly.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician