Why is my 2012 Chevy Equinox heater only blowing cold air?

You need to raise the front end of your car and open the coolant reservoir cap (not the overflow), make sure engine is cold or the coolant will blow out and scold you, but what you're looking for is basically air in the system.

Even though the coolant level may seem full there may be air trapped in the system.

To get the air out you can turn the engine on, turn heater to max heat and full speed, and squeeze on the hoses that go into the radiator and see if any air bubbles come out.

If this doesn't work you may have a broken heater core.

I just purchased a 2012 Equinox and had the same issue. I took it in and the service manager checked the coolant and it was fine. He then turned the temperature control to the cold ( blue color) and then it blew out hot air. The heat ( red color) blows out cold air. Everything seems to work fine, it's just that they are backwards. I don't know if this helps.