As if it's not enough that I'm freezing my butt off in the mornings lately, my car no longer blows hot air through the vents when I turn on the heater regardless of the temperature setting. I immediately checked the coolant level and everything checks out normal, it's almost as if the cabin temperature sensor has failed and it thinks the temperature is 100 degrees! So no matter what temperature I set on the heater it tries to cool the cabin with cold air.

Anyone got any ideas on this one?
Thanks,

Start by interrogating the ACC unit for faults. IIRC it's the same as the 9-5; press AUTO and OFF simultaneously.

Thanks Mark, I've done what you recommended and it came back with the number zero displayed on the screen for about 20 seconds and then it went off. I repeated this and it came back the same. Do you have a lookup table that can identify what this code means?

Well the good news is that the zero is the number of faults found on it's self diagnostic. Sometimes just carrying out this procedure which also re-calibrates the system can cure problems. I suppose that's too much to hope for in this case...

I'll find out tonight on my way home from work when I get the engine up to temperature and I'll let you know how I get on. Thanks for your help so far.

Look under the hood. There are two hoses going through the firewall - one supplies the heater core with hot coolant, the other one is return. Feel if both are hot - if not, the core is blocked with debris in the cooling system.

Thanks for all the replies. Resetting the ACC unit appears to have done the trick and I've got nice hot air blasting through the vents again! It's the little things in life, you know...