fans work by bridging wires, but not with new sensor...why? - Alfa Romeo Forum
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fans work by bridging wires, but not with new sensor...why?


I have been trying to get the fans to work on my 1996 gtv. I could not work out which relay was relay 99 & 100, but discovered that if I remove the plug from the radiator sensor, and connect a wire between the black and either of the other two wires, then the high and low speed fan speeds work.

To me, that means the sensor is bust, so I bought and fitted a new one today costing 21.

Still doesn't work (at least on low speed).

Any ideas, as I am confused?
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There's (at least) three working items you need to get a signal to the fan.

On the early models, the first is a sensor low down on the rad near the bottom hose (I think that's what you're referring to) - this has two switching temperatures for the two fan speeds. On the later models, the ECU just reads the temperature sensor on the thermostat and has two separate outputs for each fan speed.

These signals operate a relay (one for each fan speed). Depending on year, these may be in the engine compartment or at the top of the fusebox under the steering wheel (one yellow, one black). *If* the sensors above are working OK, you should hear a click from the relevant relay when the correct temp is reached.

The higher speed relay output simply connects the battery to the fan directly. For the lower speed, it connects through a resistor block that's mounted on the top of the fan assembly, on the engine side (rather than radiator grille side).

If the relay for low speed is clicking at the correct temperature but the fan isn't coming on, then this resistor may have blown. Turn off the engine, unplug the wires and use a circuit checker (multimeter or even just a small battery and bulb) to see if a current will flow through it. Alternatively, when you've removed the wires from the resistor connect them together, start the engine and wait for it to wrm up again - you should now find that your fan will come on at *full* speed at temperature at which you'd expect half-speed. It's fine to run the fan like that for a while until you've found a replacement resistor.
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Do you have one or two fans? if two check that the connectors to the fan resistors and to the fans so that they are properly connected (they use the same sort of connectors and may have been mixed), connectors
with brown and red wire shall go to the fans, connectors with light blue/white and white wire shall go to the
fan resistors, check also the fuse Q39 (30A) green fuse holders in the engine bay so that the fuse is not blown.

Hope it can be of some use

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