Sounds like the Blender motor door actuator for the passenger side is stuck in the Heat position.
The actuator is located behind the dash between the radio and the airbag towards the firewall. To replace it,
you would have to literally remove the complete dash and disconnect passenger side air bag in order to replace. You definitely want to avoid using the Dorman actuator and try to replace with OEM quality. I have had to replace the Dorman brand actuator twice in a year; luckily it is in an accessible area.