Exterior temperature sensor and AC

[drivin_me_nuts]

I am hoping that someone will be able to help me.

This morning I started the M5(E39) and the exterior temperature gauge dropped to -40 celcius...where it then stayed for a time. Over the next few minutes driving it gradually increased from -40 to about +16. It stayed evey though today was certainly higher than +16 today. Now the weird thing. The AC was on from the time the car was turned on, however it did not start working until the external temp gauge showed about -7. Then the AC kicked in.

When I switched the car off for about half an hour and switched it on again the temp showed -7..

I waited another hour or so and turned the ignition on again and yep, back to -40 again and no AC until the 'external temp' was about -7.

So, does anyone have any idea what is going on and what bit might need to be repalced?

Cheers

[gizmo.mp3]

Just a wild guess, perhaps the AC doesn't work below -7° as a protection measure - to stop the extra-cold air freezing internal parts of the AC system?

[dan101smith]

Sounds like the external temp sensor is up the creek. Most car aircon systems don't work below a certain ambient temperature for the reasons mentioned above.

[BlackSpider]

At the front N/S under bumper(black panel) or in the brake vent pipe is a probe-black about 35mm long,pointed one end electric connector the other-these tend to fill with water and fail,or they are torn off or the wiring becomes corroded and the pins break.
The A/c releys on this giving an outside temp,if the outside temp is below 6 degrees ish it will stop the compressor working.

[drivin_me_nuts]

...thanks for the advice. will have a dig around underneath and see what's going on.