Temp control issue

[Gfather1]

Hello, I hope someone can help me, I haven't found anything on here as far as the issue I'm having with my 03 Yukon. Here's the deal, my A.C. works I heat setting and my heat works on the A.C. setting. Defrosting my windshield is difficult in the winter because A.C. mode doesn't do defrost. Have no clue why they are switched.

[Spurshot]

That's a bit of a riddle. Some more clues might help.

 

This is an 03 Yukon. What trim level? (Climate control or manual) How long ago did it start doing this? Has there been any work done under the dash?

 

If no recent or coinciding work was done, I might be suspicious of the HVAC control panel. Ebay has a lot for sale.

[Gfather1]

It's climate control, digit display. It's been this way for at least 4 years. But I hardly drove the truck due to bringing work truck home. It's the base model yukon, I think the sky. I tried some rest today. When I turned the heat on in the front, the back and third row had cold air coming out the roof vents. When I went to a.c., the air was cold out the front vents but got colder when I turned the a.c. off.