Symptoms of bad CCU

1983 300CD. No response from CCU - no blower motor, no heater, no A/C, no defrost. No nothing.



I've checked the common-sense stuff. Fuse is fine - not blown, and made sure that it's making good contact w/ the bus. Blower motor is fine. Nothing jammed in the squirrel cage, and when I remove the blower motor and jump it to 12V from the battery, it works just fine.

No response from the CCU regardless of setting - doesn't work at low temp, high temp, low fan speed, auto fan speed, high fan speed. Nothing.

Is this symptomatic of a bad CCU? What else do I need to do to troubleshoot before I order a rebuilt unit? Not sure if the one in the car is original - I suspect that it is.