ACC Question on 1980 300d

[tex599]

Recently the a/c system only started to work when on defrost. Also had trouble shutting the car off, unless I disconnected the green vacuum
Line and plugged it. This also affected the door locks. My servo is working as it moves when I adjust the temp gauge and the aux water pump is fine, compressor comes on fine to. It seems I need to track down the vacuum leak, but not sure where to start. Any advice? Also noticed the temp sensor hose is no longer connected, looks like a piece is missing, wire is still attached at the speaker grill. How do I know if my amplifier is good. Any suggestions ?
Thanks,