I have a 2017 Chevy Silverado 1500 5.3 L with 60,000 miles on it. My problem started about 30,000 miles ago I would have my temperature preset to 75° in the morning start the vehicle and be fine drive 10 to 15 miles heater work great. Let it sit for half hr nothing but cold air would come out. I would slowly adjust the temperature and around 81° we we start working again. Hi if I drop the temperature lower than 81 it blows cold air. This happens most of the time. Sometimes I have it set at 75° start driving it turn it down to 74° and it blows cold air. And there are times when I start it no Hot air comes out until I turn it up full blast and that’s only only way it will blow heat I turn it down a little bit cold air.
