I have a 2007 F-150 King Ranch, and although the temperature would reach optimal operating temperature the air coming out of the vents wold only be lukewarm (outside temp 5 degrees). If I would turn on the AC and then back to heat it would get hot. also the "auto" setting would never warm up. I thought it was the blend door actuator. But after digging on the internet, someone posted they had similar issues and they replaced their weak battery and it fixed it. I had the original 540 cca battery in it still, So I decided to try it anyway and replaced it with a 850 cca battery. And so far (3 days) it has fixed the problem and heat works great.

I am assuming my battery was just getting weak over time and being all the electronics on the truck it just didnt have enough power left??? I'm hoping this was the fix, and that it's not just intermittent.

 

I realize this is an old thread and the original poster only has 1 post, but...

Has anyone else dealt with this? My a/c alternates between cool air and luke warm air.
It has never crossed my mind that the battery might be the cause.

any thoughts?

 

Replace your blend door motor.

That old post doesn't make any sense whatsoever. The heat comes from the engine coolant being pumped through the firewall and through the heater core. Air is blown through the heater core and into the blending unit. Maybe if you had a weak blower motor it could be related to the battery, but the water pump is mechanical and that's what drives the hot coolant around the engine bay. If your battery is going bad, it would likely be causing lots of other problems such as starting, lights, radio, etc. not working.

I can tell you I had similar problems with frequent blasts of hot air when my A/C was on, and it seemed like the climate control couldn't hold a steady temp. Replaced the blend door motor and all is better.