The porcupine or resistor is a power transistor which is terminated at the firewall by a 3 prong plug. The 3 wires are powered, ground and control voltage. The control voltage 1 to 5 volts controls the fan speed. That's where I'd start diagnostics. On a side note check your auxillary water pump and see how much current it uses or if it even works. High current > 1 Amp will cause your CCU to do funny things.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10