Dear CW,

May this find you well. When you use the term "fan", do you refer to:
(a) the blower, under the dashboard, that moves air inside the passenger cabin?
(b) the auxiliary cooling fan, in the engine bay, that comes on to help cool the engine, when the outside temperature is high?

Does the term "power unit" refer to:
(a) the ECC controller (located above the radio, in the front center console)?
(b) the blower motor (located under the dashboard, above the passenger's footwell [USA/Canada models])?
(c) the the auxiliary cooling fan (in the engine bay)?

Have you opened up the ECC and re-flowed the solder joints that:
(a) connect the relay (switch) to the circuit board?
(b) attach the main connector to the circuit board?
These joints develop micro-cracks over time, cracks usually too small to be seen with the unaided eye. Usually, these cracks will cause intermittent operation, or keep the system from working.

The fact that you refer to "repair work" - and found a partly un-insulated wire - suggests to me, that someone may have worked on the circuit board or wiring, and inadvertently damaged it. If you changed the ECC, and the problem persists, then the problem is likely to be in the wiring.

It may be necessary to trace each wire. Plainly there's a short circuit. A conductor is touching metal, either the body, or another wire.

I'd start at the area where the "repair" was done, and go from there.

Hope this helps.

Yours faithfully,

spook