driver side A/C vent blowing hot air

[Yaross]

Sirs,

I know somebody here already had same problem with one A/C vent blowing hot air (side vents on the dashboard, infront of cup holder). I tried searching but no luck. Probably using the wrong keywords

In case you know the thread, please post the link, otherwise, kindly advise.

The problem:
My driver side A/C vent recently started blowing hot air while the center and passenger side vents are blowing cold air. It occurs when the temperature knob is set from halfway the cold setting (blue colored) up to the start of hot setting (red/orange colored).

When set on the warm settings, all vents are blowing warm/hot air.
when set on halfway down to full cold settings, all vents blowing cold air.

Appreciate all your replies. Thanks!