Prius Prime heater always on even without fan on or AC on

My Prime heater is always on even with the fan turned off on the display panel. I can feel some heat coming out on the vent even with no fan on. If I turn on the fan, set temp to lowest temp, 58 degree F, I still have hot air coming out of the vent. If I turn on AC, I still have hot air out. I have to turn off the air fan, turn on Recycle mode in order to block all air to stop hot air from coming out of the vent. I brought it to dealer and they diagnosed the heater box needs to be replaced at a cost of $6000. They said they need to take out the entire instrumentation display to do the repair. I wonder if anyone has a similar problem and how did they fix it. Thanks in advance!

 

This is per the dealer:

" Found codes B1441 & B1448. Cleared codes, performed A/C initialization. Codes came back. Inspected servo motors for mechanical damage. Was unable to find damage. Require tear down to further inspect. Rec replace A/C heater box. Part# 87050-47400. "

My further findings about the hot air coming out of the vents is that when the car is in EV mode, the AC works properly, cold air comes out. As I slowly cranked up the temp, warmer air comes out of vents. When the car has used up the battery in EV mode and the engine kicks in, that's when only hot air comes out of vents regardless of AC/temp setting. I also noticed there is no air comes out on the front passenger vent even when the driver-only vent mode is turned off (this is an Econ mode in Prius Prime where hot/cold air comes out of the driver side vent ONLY to save energy).

Also, all ventilation settings are gone after the car is turned off for an hour or so. When I turn the engine back on, I have to set up the temperature, how much air flow, air vent mode (top, middle, bottom to the feet), Econ mode, etc. The settings are kept if I turn off the engine then back on after a few minutes. If I turn on the engine an hour or two later, the previous settings are gone.

 

From what I have described, do you think the dealer has diagnosed the correct problem that the entire AC box needs to be replaced? Thanks Mendel!