outside air temp inaccurate

[Jimbo]

So ever since i bought the car its never worked properly, it always displays a temperature but lets be honest its not -23 degrees outside (thankfully).

Now i have changed the passenger mirror for another one i had spare, but still no different 

Then i swapped the actual clock unit itself in the hope that there the only two parts to make this work.
I know its not faulty wiring in the door loom otherwise it wouldnt display at all. 

Mirror and clock both spares i had and unsure of there condition just kinda hoped that i wouldnt have two faulty units. 

Anyone shed any info/light on what to check next
Cheers