The fans come on low speed when the AC is at operating pressure, it takes mine about a minute for mine. They come on high speed when the engine gets over 106 deg C, that is controlled by a variable resistance sensor located about a third of the way from the back of the engine on the top of the cylinder head tucked between the valve cover and the air filter. The signal goes through the climate control in the dash (don't ask me why) which has the relay. Hi/low goes through a power resistor bolted to the body just to the left (looking towards the back of the car) of that AC cylinder thing with the sight glass on top (forget what its called).

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5 speed '91 190E 2.6 320,000 mi. (new car, fast, smooth as silk six, couldn't find any more Peugeots)
5 speed '85 Peugeot 505 2.5l Turbo Diesel 266,000 mi. (old car, fast for a diesel, had 2 others)
5 speed '01 Jetta V6 (new wifes car, pretty quick)
5 speed '85 Peugeot 505 2.2l Turbo Gas 197,000 mi. (wifes car, faster, sadly gone just short of 200k )
5 speed '83 Yamaha 750 Maxim 14,000 mi. (fastest)
0 speed 4' x 8' 1800 lb Harbor Freight utility trailer (only as fast as what's pulling it)