Outside temperature sensor - Alfa Romeo Forum
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Outside temperature sensor

Hello all,

My 155 has the digital aircon fitted. Today, the outside temperature reading became faulty (always reading -29 deg). This means that the aircon does not work properly - always heating unless set to "Lo" position (then always freezing cold). My question is:

1. Does the aircon have its own temperature sensor, or does it use the engine's air temperature sensor?

2. How can i tell if it is the sensor that is faulty (I hope it is not the wiring or the aircon unit)?



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Hello David,

Most likely it's your sensor or the wiring towards it, since the display still gives a reading of -29 deg. This is the same reading you get when you disconnect the sensor. The sensor is placed in the LH mirror (at least for LHD cars).

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Hi David,

Ivo is probably right that it is the sensor or wiring, rather than the controller. The sensor is the little black 'pimple' sticking down from the bottom of the drivers side mirror. There are a couple more sensors to find as well. On is behind a tiny fan, which you can find below the steering column, slightly to one side. This is the cabin temperature sensor. There is also another one inside the heater unit itself and this gives the temperature of the air being delivered. I think there is yet another that checks to make sure the evaporator isn't freezing.

As a short-term fix, if you can locate the connector for the outside sensor, you could put a potentiometer across it for now so you can dial in whatever external temp you think is correct! About 4k7 should do it.
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Thanks a lot for your help. You are spot on! Some moron smashed my driver's side mirror off a couple of weeks ago in a pointless act of vandalism. I haven't needed to use the airco since (I live in Scotland) so I didn't put 2+2 together. I did wonder what the little plastic bump was for. Duh!

FYI, the local AR dealer has not been able to get me a replacement mirror unit yet, and has had to put it on back order (140). It's the metal bracket which fits on to the side of the door that's broken.

I don't suppose anyone has a spare?

Didn't think so.

David M
Sean Conway
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Always wondered what the plastic nipple on the mirror was for! - mine doesn't even have aircon, so presumably it's just a blank. Had to take my drivers side mirror off last week to touch up a spot of rust that was creeping out from behind the plastic mounting. What a pain ! The thing is held on by 3 cross head screws, one of which was completely frozen solid. By the time I got it out, the head was totally chewed up. It seemed to me that there had been some sort of chemical reaction going on with the metal bracket DavidM mentions in his post. The bracket was covered in white dust, which was also present in the threads. When I put the thing back, it will be with a good dollop of copper grease.

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Hi all,
Someone crashed my drivers side mirror too; the metal bracket (it just some kind of alloy with 3 screws to be fitted to the door) was broken in 3 and I have glued it back with "Bison" (http://www.bison.nl).

The complete mirror's price at AR dealer is 165 millions of Turkish Liras (which is 150 US dollars).

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