Random cabin temperature control

Occasionally my cabin climate system decides to get stuck on maximum heat, regardless of the dial setting. A mechanic thought it was the aftermarket radio pushing down on the electrical plug in the back of the temperature control dial, and raising the back of the radio seemed to correct the symptoms for several months, but now they’re back. Turning the dial doesn’t help, removing the radio doesn’t help, turning the truck off and back on doesn’t help.

Ford has been making F150s for quite a few years. How old is yours?

Sorry.
2001 super crew, 5.4 L

I know there have been reports of broken blend doors.
Is there an easy way to confirm if this might be my problem?