2015 Yukon A/C Works...sometimes

[TheDobey]

Early 2015 Yukon that I've had since day one. The A/C blows ice cold, then if you adjust it warmer, it blows hot, and I mean hot! Rear A/C seems to cool alright. 

 

Here's the kicker: dealer diagnosed the problem to a leaking evaporator core with an estimated cost of $3,700. 

 

I can understand this if there was absolutely no a/c, but I have trouble understanding why this would be the case given the ability to cool sometimes. 

 

I was thinking blend door actuator, but wouldn't that limit the problem to just one side?