My .02
The fan ECU is actually pretty easy to get to... a phillips screw driver and a 10mm socket and you can pull the glove box out and get right to the ECU (it's a small box the size of a pack of cigarettes on the right side of the hole for the glove box once you get it out).
The PDFs should include some wiring information about the ECU, and you can check voltages directly while it's running to see what's sending signals and what the ECU is sending in response. A volt meter across the blue/white and blue/yellow wires on the wire harness showed me that I was getting VERY consistent water temp (about 2V) regardless of driving conditions, so the cooling system is doing its job. Checking the ECU output to the solenoid (I think it's the yellow and yellow/blue wires), I saw it started out a 0V, but then started turning on the fan at idle with about 4V. After driving for awhile, it would start kicking up to 7 or 8V and it sounded like a jet.
The ECU takes signal in from the water temperature, the A/C overpressure switch, and a line in from another ECU. I jumpered the A/C overpressure switch so it was consistent, and the car's fan acted a lot more normal... it still varied (which indicates that the other ECU's signal must vary with engine conditions), but it didn't sound quite like the Harrier it resembled before. I am wondering now if this switch needs to be replaced...
From a troubleshooting perspective, the more you can dig into it for first-hand data (volts and such) the clearer the answers become.
Good luck!