My '78 240d had a broken wire that I just noticed and repaired that went to the sensor on my thermostat housing. Car has been running fine and I am wodering what this sensor is for. Thanks!

See if you can trace the wire back to the source.

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84 300D, 82 Volvo 244Gl Diesel

Early EGR system sensor?

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83 SD

84 CD

On later models, there is a switch there that prevents the cabin blower fan from operating (in the heat mode) until the engine warms up.

Once again, thanks for all your replies. I went to ********az and looked under aux fan sensor/switch and it really looks like the sensor I have. I thought that only high R12 temp. sets the aux. fan on?

That is the case on some models. On other models, coolant temp is also used.