Sounds like another stuck/failed DuoValve.

Drive the car, get it heated up and if A/C blows hot, pull over, raise hood and check to see if hoses (all 3) on the duovalve are warm or hot. It so, the valve is opening when it should not.
The duovalve is known to stick open at times, if so, it needs cleaning.

Also, If power to the duovalve fails, it default to full open and you get warm air.


Video here of a Duovalve in a Mercedes...