hotpoint mistral temperature problem

Hi
I am a new user, site is very helpful.
I have a mistral FF72P 6 years old. It has the symptoms as in previous posts: freezer at -22, fridge +15. I have got as far as cleaning out fluff and removing plastic panel at inside rear of freezer compartment. Not too much ice build up. The fan in the centre is not running at all, I have tested and no supply is present. Only after reading the other posts I have realised that after defrosting I can remove the polystyrene and get access to Thermistors etc. If the fan is not running what could I test or replace.
Thanks
2nd post
After reading some more I am thinking of replacing the Thermistors What are the part numbers please.
Dave do you usually reply to these posts or is there another way of getting this info
Cheers

HELP
Have got a bit further, unplugged yellow thermistor and fan started to run, i am presuming this thermistor is the problem, whilst at it I will replace the green thermistor as well……. Any advice

Thanks
Dave