Audi A4 1.8T B8 heater issues

[Mvu991]

Hi all

I have a very funny issue, my car suddenly blows cool air when the heater is on a warm setting. So I will put my heater on, say 22⁰C and it will blow hot air, but after a while it will blow cool air. This is driving with a warm engine. Engine Guage on 90⁰C mark and not fluctuating.

Any ideas what the issue could be?

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[turtlemann14]

check temp of both heater core hoses. ima say you have a restriction in them and one will be much colder. or your blend door isn't working right