My A/C has worked perfectly well since I got the car in February 2018. I leave it on all the time Summer & Winter. Generally, I have it set on 24 degrees when I start in the morning and reduce it to between 18 & 21. Suddenly, it is behaving differently. Yesterday and this morning, I had to turn it up to Hi to get my normal morning heat and when I reduced it to 24, it started blowing cold air. This was with 6 degrees outside temperature. The only other strange thing that coincided with the A/C problem on the first day, was that on starting the car, the idle was uneven. It hasn't done this since and never before. I hope this all makes sense to someone, as the warranty ran out last month.  Thanks

When you say normal heat was the engine up to temperature at that point I.e 90C? 

 

Suggest you check if you have heat on passenger side and cold air on drivers. Close down the vents and put switch to front vents only. If the engine has warmed up then cold air on drivers side is the classic sign of heater matrix blockage due to silica bag in coolant failing. Check the colour of your coolant. It should be pink without any discolouration. Let the engine cool and remove the coolant tank cap and look inside too.  (they are stiff to undo)  

Do a flap reset / recalibration.  Run a full diagnostic scanner code for HAC errors.  Or perhaps a faulty vehicle cooling system thermostat. Stuck open?

3 hours ago, TheClient said:

Do a flap reset / recalibration.  Run a full diagnostic scanner code for HAC errors.  Or perhaps a faulty vehicle cooling system thermostat. Stuck open?

Flap reset video in this thread.