First the central locks.
The hiss is for the lock rod actuator for the fuel cap. It is faulty and has a leak causing the locks not to operate properly.
fix: replace the fuel door actuator after you test and make sure that it is faulty.
The climate control could have a vacuum leak too although the central locks and the climate control are unrelated.
It is time for a few problems I guess. Bare with it and be patient.
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
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