2013 Edge with the touch screen display. No matter what the HVAC is set on, it will randomly switch back to the Defrost setting, which changes where the air is coming out from, and it increases the fan speed. It does this repeatedly after the driver changes the setting back. It's like a tug-o-war with the HVAC system. And also, after it changes to the defrost settings, if the driver doesn't change it back to what it was on previously, it will sometimes - but not always - change it back after a while.

Is there a sensor or control somewhere that is giving the system bad info making it think that it needs defrost? Does the display need to be replaced or reset?

I haven't been able to find any info on this specific issue.

 

Wow that totally worked man life saver this just started happening to ours n were hitting them cold mornings thank God found this vid thanks man!
Kodi nox

 

Yesterday, the heat wouldn't work. Coolant level is fine. Car was driven for more than a half hour, twice, without heat. Is this a sign of a bad control unit?

 

Did you figure out and solve the defrost issue or do you have two issues now?
Do you have dual hvac? Driver and pass side can be set to different temps.
Does the AC work correctly?
Assuming the AC does work when you switch from coolest possible to hottest possible how much difference in temp can you feel?
Do you hear any faint clicking from the dash when you change the temp from cold to hot?
Can you change the air output positions and the vehicle respond to that?

 

Two separate issues now. Both HVAC related, though.
Yes on the dual HVAC.
A/C comes out cold, if that's what you mean.
We've only used the A/C on 'LO' so I don't know what would happen if we changed the temp to hot.
Haven't noticed any clicking noises.
The air output positions (dash, floor, etc) usually change when we tell it to do so, except sometimes after it reverts back to 'defrost', it won't allow us to change it away from that setting. We select another setting, but it stays on defrost. It still makes the "boop" noise to let us know we pressed a button on the screen, but it doesn't change.

 

See what happens when the AC it turned to heat for one side then the other. There are different actuators for each side.
You need to listen to the dash for a clicking noise when the temp is changed, the clicking is the actuator trying to move but the internal gears are stripped so it just jumps teeth.
All of these actuators have a internal potentiometers to know what position its at.
The defrost issue is weird especially since its intermittent, considering its not very expensive I might just replace the actuator and see if that fixes it, I am thinking its module issue but those are far more expensive to replace.
Here is the wire diagram from the HVAC module to the actuators.

 

The thing about the defrost issue is that the display (8-inch screen) does the "boop" noise and the operation light hops to defrost, as if the button on the screen was pressed. So either the screen is erroneously registering a touch, or the control unit is erroneously sending out a signal that the screen was touched and it adjusts accordingly.

Also oddly, it reverts to defrost while turning a corner often enough that I wonder if it's related somehow. It might just be a coincidence though, because it does it a lot while driving straight, too.

 

So when the HVAC changes unprompted by you to go to defrost the screen reacts like its being touched?
Take the trim panel off that goes around the touch screen, Ive seen stuff get stuck in between the trim panel and the touch screen and it registers like its being touched.

 

Correct. The car thinks that the screen was touched. And sometimes after that happens, no amount of touching the screen will make it change to any other setting until it's ready to. So maybe the screen thinks someone is resting their finger on the screen (trim panel, or faulty touch screen), or the control unit has a glitch where it reacts as if someone touched the screen, but they didn't.

 

Ok so remove the trim panel that goes around the display and wait a few weeks to see if it stops happening.