OK
My bad for not writing up the full history... my car had a heart transplant a few months back, and ever since then both the heater and air con have not been working where they both had been previously. Hence my thinking that its most likely a wiring issue.
First thing I did was check appropriate fuses: all good. Fan also works (blows ambient temperature air through the vents), so thats not the problem.
Removed the electrical connection from the heater valve and used a multi-meter to check voltage of individual wires as well as voltage across the connector terminals when car was running and up to temp. The positive terminal/wire shows 12 volts but the neg terminal shows nothing and there's no volts across the connector terminals. I COULD check 100% that this is where the issue is by plumbing a dummy wire straight from the neg battery terminal to the connector and hooking it back up to the heater valve. If heat works, then the neg wire is the issue... but that doesn't explain lack of air con??
I suppose my plan for today is to trace the negative wire backwards manually, but I would have preferred to find out where it is connected to using wiring diagrams and/or other ppls knowledge. Presumably there is something electrical between the heater valve and the battery that the neg wire runs through. Anybody know what it is? From the wiring diagram and my limited mechanical knowledge of the heating system, it looks like:
Battery ---> fuse ---> heater valve ---> blower motor ---> blower relay ---> Ignition??
NOTE: This is the first time I've tried using wiring diagrams for anything other than hooking up a stereo. I believe I may be wiring diagram illiterate.
I had thought maybe there was something referred to on the wiring diagram as the "Temperature wheel switch" and I had thought that perhaps this was the temp dial on the dash... so I went looking on various threads until I found this:
http://www.318ti.org/forum/showthrea...obs+new&page=2 I thought it might be a good idea to double check the bowden cable mentioned in this thread since it seemed like a fairly common problem, and seem to recall my heater wasn't as hot as I thought it should be when it was working previously (although I knew sorting this out wouldn't fix my electrical issue, of course). I pulled out my glovebox and went poking around, then realised that of course my BMW is right-hand drive, so I should be looking on the driver's side (D'oh!).
So now my 318ti is missing a glove box, clock and head unit, and I am no closer to sorting any issues with my heater or air con. Joy!
I'll post this somewhere more appropriate in the forums so that I might get more responses, but if you have any thoughts/suggestions, feel free to contribute
