A.C. question 85300sd
 

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.:mad:

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

Could not find
 

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.

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

Still need help
 

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.

Do you have your wiring diagram in hand? if not what would you do with any info someone might give you. The ETM has pictures of the locations of all the parts in the circuit.

Service manual
 

I have a service manual, but it is hard for me to understand. I am still in the learning stage.

You're getting into very detailed checks with a voltmeter and the wiring diagram for the vehicle. And you'd need to understand electrical schematics to get to the end of this road.

But, did you check to see if the blower functions on full defrost?

Defrost Cycle
 

The blower will not work on the defrost cycle. The only way I can get the blower to run is to run 12 volts straight to the motor. Thanks for your help and suggestions. Any more suggestions are more than welcome.

Did you ground the wire at the thermostat housing to see if the blower will work in this condition?

Blower problems
 

Yes, there are two switches at or near the thermostat, and I tried both of them. Still no luck yet. Thanks Jack

The problem is likely the CCU or the temperature control unit. When the SD suffered the same issues, I replaced the CCU and the blower properly ran again.

There may be some detailed procedures to test the temperature control unit.