Can any one out there tell me if the blower and A.C. has a hidden fuse somewhere. My fuses in the box are ok. The mono valve is working. My blower will not come on. I can make it run when I apply 12 volts direct. The air condition has been working fine until now. Help Please.

Make sure the resistor block is plugged in. It's the toaster looking device by the coolant bottle.

I looked for the resistor, but could not locate it. Does any one know exact location??? Desperate. Help!!!

The lack of a functioning blower on an SD can be one of many things:

1) CCU
2) Blower
3) Temperature controller
4) Resistors
5) Coolant temperature switch
6) Fuse


If you've replaced the fuse and have applied 12V to the blower, you've eliminated items 2 and 6.

If you ground the wire that sits near the thermostat housing, you can see if this will start the blower........or not.

Then, set the CCU on defrost. See if you get anything out of the blower at that setting.

I had a similar issue. Took awhile to finally track it back to the CCU itself. It could also be the resistors, but, usually the blower will work on the high speed setting as the resistor are not used.

I'll add one thing that kills blower operation, defective ignition switches. Usually a little wiggling of the key will confirm it.

The most common causes though are fuses and the blower itself.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks Steve..........I forgot about that ignition switch.........those electrical contacts get old after 24 years in service.

How do I check the CCU, and I still cannot find the resistors mentioned. I hate to be a bother but I need some more help. Comments and suggestions welcome!!!

the resister on 84 and 85 MB's are on the passanger's fenderwell, a metal box with wire coils in it. open on one side, and has holes in the top and side I think... open your hood, and look there.
John.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

This has been a great informational source. The only problem I had was with my ignition. I guess the ignition is getting old, because if the AC does not turn on, I just wiggle the key and it kicks on just fine!

Now to find out if it is worth to fix the ignition problem!

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1985 300SD - 167k miles
1992 F350 7.3 (Soon to be converted to 2 tank Veggy/WMO)