Why are you resoldering the CCU? If it did fail, usually a seized aux water pump is the culprit. Disconnect the wiring harness from the aux water pump, and do the following test..........
Before disconnecting the CCU...........
Using the harness attached to the pump and your car battery connect black to positive and brown to ground. Does the pump run?
Re-attach the harness. Turn the key on, do not start the car. Set the CCU to defrost, the pump should run. Set it to any of the two buttons right of the defrost, but not econ. Turn the temp dial as if you were increasing the heat level, the pump should run.
If the pump is siezed, replace it and do the 1 amp fuse mod. Do the 1 amp fuse mod anyway. You will need NAPA # 7823101 (Marine grade fuse holder) and a 7821042 one amp fuse. Splice the fuse holder into the black wire, if the pump does seize it will blow the fuse and not toast the CCU.

Tell us more what the problem is and we will help. There has been quite a bit written about the Type III climate control on this list.

Alan

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'82 240D Stick
'85 300D Auto
Drove my first MB at age 16 1960 300SL W190