Have you asked a BMW dealer to take a look? I know I immediately think
"it's going to be expensive if I go there" but if this is something that
is spoiling your enjoyment of what is a fine car, I'd bite the bullet
and ask them to take a look and "advise". My local dealer does a
slightly reduced rate for "older" cars (maybe over 4 years).

I'll suspect a problem with the water valve who operates intermittently,
look for a bad connection (broken wires, corrosion,etc)
If wiring are o.k,  pinch temporarily the outlet hose with a clamping device
and drive the car for a week or so, until you're
convinced.
The other thing that comes to my mine is the way you use your a/c. You
didn't tell but as a reminder setting temp. to the lowest cold side (16°C)
means that the a/c compressor is working "full blast" all the time and with
good humidity the evaporator may froze, given you then...warm air. That will
usually happen if outflow air is restricted (open at least 2 outlet in
cabin) or inflow air that is suppose to go trough the evaporator is
restricted (have you changed both microfilter lately) or when you use
"recirc" for too long.
BMW recommend to take care not to use the middle dash "air stratification
outlet" in full cold air (blue side) with the oulet pointing downward the
center console, because the air flow will hit the console and swirl around
and foul the inside (cabin) temp. sensor to the point that it will shut the
a/c and start the heater. The climate control module (IHKA), who lay down
the console, has a
fan inside to suck the cabin air trough the the temp. sensor, so you get the
picture. I know that it's true because similar thing happen to me but it was
the other way. To make a short story, it was  (canadian) winter time and I
was enjoying the warm air from the heater. I stop for gaz and bring back a
coffe that I put in the can holder. A minute later when I hit the road cold
air start pouring on
my face and my feet. I try to figure out what was happenning thinking I'd
just lost all my eng. coolant etc...Then, while grabbing my
cofee, I realized that that hot paper cup was against the inlet grille of
that inside temp. sensor fan. So that little fan really work.
Thing about it we never know...

Sylvain

Sorry there Jon, but welcome to Beamerworld.   That's just the way
it is with these shitty cars.   I could sing you a similar song (but
longer)
about my Beamer.   But I will say that I actually have never had to
recharge the AC in this car, in the six years I've had it.   I have had
THREE separate electrical failures in the period though.  One was
a blower motor replacement (warranty), another time they charged me
a few hundred $ for replacing a resistor, and the third time, I did
the repair myself with the help of a Website (Less than $5).

I'd take it to a good independent BMW repair shop and let them look
into it.

--------
THE ISRAEL LOBBY: Does it have too much influence on US foreign policy?

The London Review will be hosting a debate on 28 September in the Great

Hall, Cooper Union for the Advancement of Science and Art, Cooper
Square, New York.  Go to the link in my sig to reserve tickets.

-----
Kill ratio of Palestinian children to Israeli children 5.7-to-1,
Israel's favor.
Kill ratio of all Palestinians to Israelis: over 3-to-1.
---------
http://www.lrb.co.uk/v28/n06/print/mear01_.html
----------
"Don't worry about American pressure on Israel. We,
the Jewish people, control America, and the Americans know it."
 ---Israeli Prime Minister Ariel Sharon, 2001

Jon...

Did you find out what your problem with the AC was?  My 735I is doing the
same thing with blowing hot air with the AC on... In Texas... that's not a
good thing this time of year...lol