01 thermostat knob sticking

[DougieD1961]

When it's cold, the temp control knob on my heater/AC acts like it's spring-loaded. I turn it, and it makes the racheting sound, but there's resistance, and it pops back to its original place when I release it. Eventually - when the interior is warm - it functions normally. Is it the heating unit, or a cable or something that is siezing? Thanks in advance.