CCU, again - PeachParts Mercedes-Benz Forum

hitwtom · #1 02-17-2007, 10:49 AM

Hate to keep bringing this back up but...Last night I got a chance to do a little troubleshooting when I got home from work. Removed the panel under the passenger side dash and tapped the fan housing=nothing. Pulled the 2 pin plug from the fan and read it with my digital meter=0volts. Next I went under the hood and checked, starting with the #8 fuse=12.8VDC, pulled the wire off of the thermostat housing, inspected and re-attached, pulled the plug(2pin) from the mono valve, checked and re-attached. Back inside still nothing. I then shut the climate control switch off, then went to defrost. The fan came on. I again checked the 2 pin connector from the fan and read 12.8VDC. I then switched to the ECON setting and the Auto on the fan, and everything worked normal (vacuum pots switched to air ducts etc.). This morning (13 degrees outside) car started right up after glo plug light went out, no fan on defrost though. Went back inside to get ready for work and get a cup of coffee. When I came back out,(about 15 min.) still no fan. Switched system off, then to Defrost and the fan came right on. After the windshield was clear I switched to the ECON and everything worked. At lunch time today I went out. No fan, system still in ECON, about a mile down the road the fan kicked in and everything was working. I should add here that my temp gauge never gets much higher than 50 or 60 (Thinking I need a thermostat)
Questions- Where does the wire from the thermostat housing go? If I ground it, should I get voltage to the fan? Could that switch/sensor be bad? What about the wires on the Mono valve? What do they do and how can I check them? I'm thinking my problem lies in the electrical portion of the system under the hood but may still pull the CCU if I get time this weekend.
Thanks again,
Tom

captainmonk · #2 02-17-2007, 11:33 AM

my sdl has a switch that doesnt let the fan come on until you hit 50-60 degrees dont know if they all do or not but i'd fix the thermostat b4 i look further

hitwtom · #3 02-22-2007, 09:36 PM

Finally got to work on it again tonight. Again, started with my digital volt meter at the fuse panel, all was OK. Checked the blower resistor (spring looking box on right inner fender ), no voltage. Pulled 2 pin plug from fan, (with CCU in defrost-default high fan) no voltage. Kinda narrowed it down to the CCU itself. Removed the CCU and checked multi pin plugs for voltage, 12.8vdc on several pins(not sure which ones or where they go) took the CCU inside and re-soldered solder joints, re-installed CCU. My fan works now!

Unfortunatly I now don't have any lights in the center dash (I tried to check everything before I put it back together in the dash. I had voltage at the light sockets to the CCU and the octapus bulb, however no lights. I doubt that they are all bad but I guess I can replace them and see. Any other ideas on this? I still have instrument cluster lights. Where can I find an electrical schematic vs. a wiring diagram?