Front a/c works off and on

My rear a/c works perfectly. My front a/c will work all day sometimes and other times not at all. Some days it goes back and forth from hot to cold. I've checked the pressure and refrigerant levels and they are normal.

I've read posts online and seen everything from blend doors and actuator motors to evaporators and thermostatic switches, but, none of the symptoms for those items quite fit my situation.

Any suggestions?

Thanks.