Recently had a mare with the Aircon not working. Got it fixed in the end - weeks later (wiring fault somewhere). Since having it back, the thermostat on the dash isn't always giving me a reading, but the Climatronic one is working fine. 

 

Are they linked? I don't want the engine to be running too rich or anything.

 

Sorry if this has been asked before but couldnt find anything 

I'm not sure you mean thermostat.

 

On the dash there is the coolant temperature and the OBC also shows the outside temperature.

 

Assuming you mean the OBC outside temperature, then in my experience this always shows the same temperature as the climatronic unit. No idea if they are both linked to the same physical sensor or not. I don't think a fault with that sensor/reading would affect the running of the engine though.

Yeah not the coolant dial, but the outside air temperature. Matches the reading on the Climatronic but has a decimal point.

 

I think the OBC reads the outside air temperature and if it's super cold then it runs a bit richer to compensate, if it's doing this constantly it can cause a few problems (I had this fault with an old Ibiza, ending up in cutting the cat out).

 

I'm not sure if one reading is solely for the A/C and the other is speaking to the engine, or if it's linked or just for driver info 

The ECU controls the fuel mixture not the OBC. I'm not sure if the ECU has an external temperature input.