Recently had service and MOT, no issues but this past few days the blower, regardless of speed, blows only cold air, heating is fine without the blower fan on, but switch to demist and everything blows cold. 
I did see something the other day about this but can’t find it now. 
Any ideas why? Pollen and cabin filters replaced as part of service, everything worked.

22 minutes ago, Jonboy55 said:

Recently had service and MOT, no issues but this past few days the blower, regardless of speed, blows only cold air, heating is fine without the blower fan on, but switch to demist and everything blows cold. 
I did see something the other day about this but can’t find it now. 
Any ideas why? Pollen and cabin filters replaced as part of service, everything worked.

 

By cold air, do you mean ambient air, or chilled air obviously cooled by the air con unit.

Have you tried switching the air off, so you can test for chilled air or ambient air.

 

I recall something about a flap valve. I'll try and find it for you.

2 minutes ago, Rojie said:

 

By cold air, do you mean ambient air, or chilled air obviously cooled by the air con unit.

Have you tried switching the air off, so you can test for chilled air or ambient air.

 

I recall something about a flap valve. I'll try and find it for you.

 

Try Martin Sweeney

Everthing is off. No AC light, No Auto Light, No Front or Rear Demisters just one recycling lamp which doesn't seem to want to go off. Have closed vents in the dash.  Feet stay relatively warm. Colder air causing windscreen fogging use delisted high speed cold air blowing onto windscreen, clears the screen but chills the car. Switch off and press AC button, adjust temperature to 22 degrees fan/blower on level 3, cold air blowing onto feet and if opening the vents in the dash cold air blasting onto hands and face. As I said earlier, heating worked fine after the service, demisters weren't needed at the time.