climate control issues
 

1982 300sd. More often than not, i have no blower motor. No function when high or low selected on fan speed. Occasionally works when in automatic mode or defrost. Never stays working for more than 5 minutes. Usually only works when car is first started. Given the symptoms, I am pretty sure the ccu has bit the dust. I am going to try to pick a used one, any other possibility's or more common failure points?

Sounds very much like a pushbutton controller. Many are repaired by resoldering the joints where the circuit boards meet.

Did you test for voltage to the fan motor?

worn brushes could also cause intermittent function. it's so easy to check voltage on the SD, just drop the kick panel, and take the cover off the wires feeding the blower, then check for voltage when the blower is supposed to be on... if it's hot, then it's the blower, not the ccu.

I have an somewhat interesting related issue with the blower fan motor in my 83 300SD. When I turn right, it turns off and makes a noise that sounds like it might be turning very slowly. Then it kicks back in when I turn left. Doesn't matter how I have the CCU configured.

I took the motor out and jumped it with a battery back and tried shaking it around the best I could and couldn't duplicate the problem.

Cleaned up the motor with compressed air and reinstalled and for a while it worked ok.

Have the thing parked in the garage now with the fan working, so obviously I have power going to the motor, once I duplicate the problem again I will check for power again.

But absent of that any initial thoughts on if it would be the climate control unit or the brushes in the motor as the most likely culprit?

I changed the brushes out in the blower motor and in six months, the bearings went out. So to finally be done with it, I changed the motor out entirely.

It's up to you, but it sounds as if the bearings might be on their final leg.

Hadn't thought of the bearings, but it makes sense. I can smack under the glove compartment and it will turn back on too.

To the OP--try hot wiring the blower directly to see if it stays running. If it does not, problem is not in the CCU but in the blower. Could be failing brushes. Common problem.