I have a 15 year old GE side by side that can keep the fridge side at 35F but the freezer side never gets below 20F. Mostly it hovers around 24F.

An allegedly trained repair technician diagnosed it and said to replace the main control board. Did that and it didn't help. That technician couldn't even find the circuit diagram. I found it in 4 minutes.

The thermistors measured low, so I replaced the two in the freezer compartment. The evaporator coils started clogging with ice and I discovered the new main board had burnt out the defrost heater, so I replaced it. It no longer ices up. I replaced the overheat thermostat because I was running out of things that could possibly be broken. No change.

Here's what I know is working: the damper door between the fridge and freezer sections operates fine, and opens or closes in response to the fridge side front panel setting. Both the evaporator and condenser fans are operating fine, visibly spinning. The compressor operates fine, though it's a little bit noisy because it has a little more coolant in it than it should. The low pressure line in the back outside of the freezer compartment partially ices up. The ice maker works fine, though ice more than a few days old partially melts and clumps up because the freezer compartment is never cold enough. The water and ice dispensers work fine. It's on its third ice dispenser door solenoid, the first two having rusted solid. The door seals and ice dispenser door seal are perfectly intact, and the recess heater loop that keeps the freezer door from frosting up in the dispenser recess works fine and don't seem to be too hot. All of the lights, both interior and exterior work fine, and shut off when the door switches are closed.

The only things I haven't replaced are the thermistor in the fridge side and the small circuit board behind the temperature control knobs, both of which appear to be fine because of the fridge side temperature and the behavior of the damper door in response to changes in the settings.

What could possibly be wrong that prevents the freezer from getting down to the -3 to 3F it's supposed to be? I'm at my wits end, and ready to strip all the parts out of it and junk it and never buy another GE appliance again.

Any help that isn't a regurgitation of the top 5 things that go wrong with fridges would be appreciated.

Power in the house is exceedingly stable and good quality. I have multiple uninterruptible power supplies feeding computers in the house, including one commercial grade supply. They monitor power quality, and alarm when there's any deviation. The commercial grade supply even knows how to email me if it senses a problem with line power. There have been no incidents.

I bought it from Sears. They want to charge me money to even talk to me, never mind diagnose it. I've already paid money for a diagnosis that was wrong. I'm searching for a little wisdom of the crowds here.