BMW Repair: e32 735i A/C troubleshooting, vacuum leak, brown wires

Question
A/C module only turns on when in high mode with hot air coming from defrost vents above dash. I had the car topped off with R34. Then even bought another A/C module from ebay and checked it in another e32 and it is good. I read that it could be the sword. Compressor is good. Your opinion of possibilities? Thanks. You helped once 4yrs ago.

Answer
I doubt it is the sword.The function of the sword is fan speed but does not control direction of air flow.Had this been an earlier "7" I would suspect a vacuum leak,but this being an E32 the vacuum thought has been replaced but electrical motors.When BMW's have a fault with the heat/a-c it goes into a fail safe mode which sounds like what you have,it directs air flow to the windshield so that the operator will still be able to see when driving if a problem occured.You have replaced the module with a known good unit and the problem still persists.I would begin checking your grounds starting at the battery.The body ground is the braided wire that is pigtailed to the ground wire.If it is green at all,replace it.The connections at the battery also need to be clean.I don't have the year or what engine is in your car so my best advice is to check the grounds.Even under the dash bolster.Ground wires on BMW's are brown wires.