I've got a 2010 FX4 that I bought in September. My AC worked fine. When the weather turned cold and I started using the heater, that seemed fine too. But I've just noticed the temp control dial isn't working. No matter where I turn the dial, including ALL the way left, I get flaming hot heat...Even when I turned the heater off, and tried turning the AC on I get hot air only.
Anybody have a clue where I should start??
Thanks.

 

Check the A/C heater control motor located below the air box. (passenger side floor) Should be a fuse for it. It closes the "BlenDoor" shutting off air flow over the heater core.

 

Thanks Marc, I'll check that out.

 

Did this solve your issue? My 2010 XTR Crew Cab just began doing this today. It was cool this morning so I put the heater on for my short drive to work. At lunch - 4 hours later - it was warmer out and I was hot from working so I put the AC on. It continued to blow HOT. I tried just the vent with no AC and that too was hot. The dial was all the way cold and still no change. I checked the fuse at #15 for climate control and that seemed fine.