06 explorer passenger side AC gets hot then cold intermittently

[sbdjersey]

My daughter's 06 explorer passenger side ventilation gets hot intermittently when in AC mode. Passenger side temp is set to 60 degrees (lowest setting). Driver side cools fine and passenger side cools fine when not stuck in heat. AC charge looked good. Does anyone have any idea what might be causing this? Thought it might be a mixing door or temperature sensor but I have not worked on this before. Any help would be greatly appreciated! Thanks.