1998 740 cabin heat on all the time

The heating system throws heat all the time at the defrosting outlet even when the temperature settings are set to colder than outside temperature. The controls are set on auto. The cup holder is broken and heat also comes out there.
Turning on the air conditionning reduces the heat emittion but not completelly.
This is exxxtremelly annoying: hot air in the face and regulated air everywhere else.
Has anyone encountered this problem? If so, what is the fix?
Regards,
JR

There are a couple of guys in the Netherlands who have a website with numerous fixes with descriptions and photos for 7-series BMWs. Their cars are older than yours but probably the heating and air conditioning systems are very similar. Look under "IHKA Components". Email them if you have questions as I'm sure they'll be glad to help. The link is here:
http://bmwe32.student.utwente.nl/

Sounds like a door is not functioning properly. If it is vacuum operated, the door that directs the air to the defroster is not getting vacuum( vacuum leak, vacuum pot not working, etc), if it is cable operated, the cable broke, pulled out or came off, or the switch (or lever) that control the blend doors is not working properly. Or even a seal that seals the door when shut is dried up and broken off (usually made of light foam) and letting hot air through.