Front A/C works some days and not others

My rear a/c always works perfectly. My front a/c will work all day sometimes and other times not at all. And some days it works off and on as you drive. I've checked the pressure and refrigerant level and everything is normal.

I've read a number of online posts and I've seen suggestions from actuators and blend doors to evaporators and thermostatic switches, but, the symptoms for those items don't seem to quite match my situation.

Any suggestions?

Thanks.