Either full hot or cold - Hi all, new to the forum and looking for some help please. I've got an 03 silverado I've owned since new. The issue is, ...

Hi all, new to the forum and looking for some help please. I've got an 03 silverado I've owned since new. The issue is, the heater is either full hot or full cold. If its selected to 90 on both sides I get heat but if any other temp is selected, it just blows cold air. Everything else works,ie defrost, and all the other vents. I've been searching this problem but finding only problems relating to side to side issues. Any help would be greatly appreciated!

not sure if i can help but i can tell you i can sorta relate. my 05 sorta does the same thing; 90 on both sides is hot and then i turn it to 89 and it blows cold air. It seems the problem goes away after a while though. after im driving for 15-20 miles it starts to work normal. and then other days it works like it should the whole time.