We've been dealing with our 2014 Impala 2LTZ not having any heat or very little in the cabin when using the "Auto" button found on the heater control. During the recent dip of temps in New England to negative and single digits, I had enough shivering while going anywhere. Under the auto setting, the fan would speed up to near max speed, but the fan would sound like a vacuum cleaner with your hand held over the hose. I started to play around with various controls and to my surprise, when I selected floor/vent or vent or floor, I was getting sufficient heat.
So when the time came to bring the car in for some other work, We mentioned the heat difficulties/behavior to the service adviser and asked them to take a look at it. When it was all over, a software update was applied to the heater control unit. We had a couple really cold days since the work was done, and I must say, the difference is AMAZING. There is plenty of heat now to keep us warm and happy.

 

Sometimes you get lucky and get a tech that actually knows what he is doing.

 

rarely but sometimes.