A burned relay contact may have enough resistance that the motor will not start from a dead stop but will continue to run once started using another relay. That may be what you are seeing. Another possibility is that the other modes are starting the fan on a higher speed, which provides more voltage.

Try this experiment: With the ACC off, press the High speed fan button, the top one in the column of three. Then turn on the ACC by pressing EC on the CCU. Does the fan start?

Either way, it's probably time to pull the CCU and check all of the relay contacts. Carefully burnish with a relay tool or light emery cloth, then clean and reassemble. Check for fried traces on the pc board while you are in there. Not much else in that unit.

BTW, have you installed a fuse in the aux water pump circuit yet? About 2 amps should do, will save the CCU should the motor seize. See W123 aux water pump fuse install w/pix
for details.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
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