We have a GE Profile side by side (TPX24BIY or maybe TPX24SIY) which is
plenty cold in the freezer side but barely cooling on the fridge side.
It's running continuously.

I know from past experience these models are very touchy when the condensor
gets dirty but I gave it a good cleaning about a week back and they
normally go back to normal operation within a day or two but not so this
time and as I said the freezer is solidly (below-zero) cold. Refrigerator
is only 40-50 range.

Before I call in the pros I want to check on the defrost system since I've
read that a defrost failure can account for this problem. Where is the
timer on this model? I don't see it on diagrams. I want to see if there
is a problem with the timer or the defrost heater. If nothing checks out
there then time for pro help. But where is it located? There are no fancy
electronic controls on this model.