New problem. Only heat comes out of vents. Temp control knob set to max cool doesn’t doo any good. Need to run A/C on Max to make interior comfortable.
It sounds like you have a faulty heater control valve. Go on YouTube and see Chris Fix go through a diagnosis scheme that includes the valve. I believe he shows this on a system similar to yours.
It was nice of the Ranger to have this problem now, rather than August 
Do the engine compartment fans turn on whenever the AC is enabled?
it could be a stuck blend door. blend door actuator could be bad,
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this is for a 1996 ranger but you will get the general idea.
On a Ford Ranger it’s a blend door, and they do break.
There is a heater bypass valve to shut off the water to the heater core, but it only activates on Max A/C
Ford Rangers only have 1 fan, and it’s belt driven.
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Belt driven engine fan? Surprising for a 2006, thanks for the info, good to know.