Why is my heat only luke warm?

04 Toyota Matrix XR
My air nor my heat was working at one point. No clicking or anything like
that. We have gone through lots of different tests for the usual suspects with
ac/heat issues. Topped off coolant, new serpentine belt, check low-side and
high-side pressure, used AC charge, I thought we did some sort of blower
motor test at some point (it's been a long batte).

Well, we replaced my radiator for unrelated reasons and did a complete
flush, and now the AC seems to be colder and the heat a little warmer, but if
it were cold out- I'd still be freezing.

We've noticed that the temperature knob kind of spins freely. If you move it to
all the way cold and put light pressure on the bottom of the knob, it pops and
spins to mid cold/warm. As if there was a spring in it. We can turn it to the far
side of cold or warm and get either cold or warm-ish air, but there is no real
difference in temperature in between. Do you think that could be related to
the issue? The next culprit we though was blend door or possibly a cable to
the knob? Ideas? I don't want to freeze this winter.