When I turn heat control up or down it stays at one temp

What is your question?

On my 2007 Mercedes Benz S550 when I turn temp up or down on climate control, temp doesn’t regulate. I have the setting at 78 degrees and it’s blowing hot air and when I turn it down to 63 degrees the temp doesn’t change unless I turn it to the low setting which I believe it the turns on the AC which is cool and AC pressure when I check is normal.