Great! I'll give that a try in the morning on a cold startup.

Never got the chance unplug the Aux.water pump. Today was the first time my W124 has failed me mechanically on a long distance trip (CT to Tuxedo Park, NY). Seems as if I'm experiencing the swollen brakeline symptoms. Early in the trip the car started to make a very strange noise, almost as if one of the wheels was not balanced correctly, a sort of harmonic low sound. I pulled over and kicked the wheels....maybe Firestone didn't tighten the lugs, not it......I then felt that the front passenger wheel was very warm. Emptied a bottle of poland spring on it only to watch it dissapear as steam . Thankfully I was near my girlfriends house so I limped it there and swapped cars, took her fathers Buick. After the trip I limped my car home slowly, half way home the blower cut out........and it cut out for good! Ahh whats that the old timers say? When it rains it pours? I just ordered new brake lines for all four corners and splurged for a new blower motor regulator, keep your fingers crossed for me!

Went out today to put the new regulator in as there is quite a snow storm on its way. Unfortunately the regulator did nothing, I'm going to open the CC unit and look for anything out of the norm. If anyone has any suggestions for me at this point, consider them greatly appreciated. Also if any of you guys would be willing to help a fellow forum member out and have a spare CC Unit laying around for a good price PLEASE let me know. My car drives me nuts, but I'll never part with it !

I have a W116 79 300SD with exactly the same symptoms. As does another member who has been posting on the diesel discussion. If you get yours diagnosed please let us know. I have a plan to blow a heat gun on various components of the system in cold weather to see if I can figure out what is causing the problem. I switched out the amplifier and it made no difference. If temperature is above about 25 degrees or so, blower works flawlessly.
If I can't get mine diagnosed I may wire a separate circuit to the blower with a manual switch because I know it blows if I feed it 12 volts directly. It's not the coolant temperature cut out switch because that is bypassed in the defrost mode. I'm thinking it is a bad connection or cracked solder joint that is separating enough in cold weather to stop conducting.
The 116 has the earlier servo system but the problem also seems to occur in later 123 models without the servo since people with later 123's have reported the same problem.
It's a damn irritating problem.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I a having a similar problem on a 107 and it seems to be the blower motor/chassis connector - reseating it helps for a while. I'm going to look into cleaning it soon.

__________________
86 560SL
With homebrew first gear start!
85 380SL
Daily Driver Project

http://juliepalooza.8m.com/sl/mercedes.htm

Lots of different system types mentioned in this post. On the later 123 system, a common blower problem is cause by corrosion at plug for the blower resistor block located on the passenger side fender well in front of the expansion tank. Frequently, the male and female pins need to be cleaned and the female pins need to be carefully squeezed tighter with pliers. Mark

hi on my 1980 450sl i replaced the servo with a used working unit and a used climate control . first turned it on but only defroster blew air and the thmb wheel only stayed hot in ether positions. i replaced the amp speed control unit under the glove box . turned it on and the temp changed also the hi lo and by worked. the only thing the blower when in hi mode was not like in def mode
the system worked for 10 min then only defrost. , took out the amp box and opened it to see the transistor was toasted . what could cause this to happen,could the parts be that fiff, my old servo said 102 the replacement said 104 inside is the same
any help please also the door locks dont operate vaccume issue , the air dosent blow out center just top and bottom

A seized auxilliary water pump will take out the amplifier. Check your pump. You should fuse the auxilliary water pump with a low amperage fuse so that if it seizes and starts drawing excessive current, the fuse will blow before the amplifier burns up.
Search on auxilliary water pump fuse kit. There's a member here that has a nice little inexpensive fuse kit to solve the problem.

Here it is:
1 amp fuse link for w123 Auxiliary Water Pump – Plug and Play!

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13