1995 f150 heater nightmare
 

I am hoping someone may have some valuable insight here.
Problem: There is no hot air blowing through the vents. One day last winter it just quit without warning, it didn't put in its two weeks, and wasn't polite enough to request a resignation. The blower works, but when the heater is on it just blows outdoor temperature air through.
Things I know: I am not low on coolant. The hoses that go to and come out of the heater core are both hot, so I assume that the heater core is not the issue here. The AC works; when I have the temperature on cold, it's cold; when I have it on warm, it's less cold; so I assume that the temperature control is not the problem.
Could it be the heater control vacuum thinger-jigger?
Could it be something else?
Could my truck have a personal vendetta against me because I am about to sell it because I have a kid on the way and need a back seat?

Temperature control cable.

Awesome, I'll check it out.
Thank you.