I have an O2 sensor out which I just bought the replacement, and now out of nowhere my heat stops working. The electronics where I select the temp, output, fan speed, etc. seems to be working and it will switch from defrost to floor, to mix, etc. but it all comes out the same cool temp. I am replacing the O2 sensor today and don't know how that would have anything to do with the heat but ... could it? If not, where do I start looking to fix this heat problem? It is in the 20's so heat is kind of important.

It just worked one day and didn't the next, it wasn't a gradual thing. No signs of coolant leaks anywhere inside or outside the truck.

Thanks in advance for any help pointing me in the right direction!! Oh, and happy Valentine's Day guys!

 

The Oxygen sensor has nothing to do with HVAC.

If you're not getting any heat, and your cooling system is intact, the blend door may have gone to a better place.

 

That was kind of my thought. I have messed with this on older cars but, how are these run? Vacuum, electric? Just crawl under the dash and have someone switch from AC to heat and listen and look?

 

If you're using the web browser, and not the phone app, search for blend door. IIRC someone has a how to thread about it.

https://www.f150forum.com/f3/blend-door-11075/

Vacuum powered, see if there's a leak in the line.