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Whilst poking around the engine bay this morning I discovered a loose tube and I'm guessing its female partner. It disappears inside thru the firewall where the headlight adjustment tubes are.

I'm guessing its for vaccum but what does it control?

Runs to the interior temp sensor for heater control, under lower dash panel. Connects to one of the nipples under centre of manifold

Page 7000-3, figure # 5

http://wedophones.com/Manuals/BMW/1986% ... Manual.pdf

Hey thanks for responses. This might answer a few questions about heater issues.

jps635 wrote: ↑Mon Jan 13, 2020 5:46 am Runs to the interior temp sensor for heater control, under lower dash panel. Connects to one of the nipples under centre of manifold

Fascinating! Are you able to explain the role of a vacuum pipe in relation to the temp sensor and more generally in relation to heater control?

# 10 part
https://www.realoem.com/bmw/enUS/showpa ... Id=64_0467

Page 6413-0

Follow heater regulator- measures cabin air temp (lower left) GN/BK wire to air door control unit. Open and closing.
Also feeds A/C selector switch for heat & A/C. Guessing it opens and closes heater valve and on & off A/C compressor
along with controlling vent flaps.

On page 6413-1 the heat regulator also controls fresh air control unit.

Hope this helps a little.

https://www.millerperformancecars.com/f ... Manual.pdf

Phil, see below

jps635

That's a great diagram, where did you find it and is there any more of that style available?

Thanks
Bob V

Bentley manual. There's a few similar type diagrams for various systems. Makes it easy to understand what's connected to what.