Fridge does not get cold , " E4" displayed on

I would say if this was a manual model, that it was your defrost timer. When you get a computer board involved, I'm just not sure.
Have you tried partselect.com ?

Try lower either the thermostat setting or the airflow control to the refrigerator to see if the temps are lowered.

I just had the same problem with my Samsung. OF means it is in demo mode. On my fridge I had to press "Energy Service" key and "Power Freeze" key simultaneously for at least 3 seconds to bring the fridge out of demo mode. Hope this helps.....

adjust to the nip in control

Try lowering your freezer temp and it'll probably lower your fridge temp.... Give it a few hours before checkign again.

unit not defrosting. or damper not opening

If you're handy with a soldering iron, it's possible to 'trick' the fridge into cooling down a few more degrees.

Long version:
If you open the door to the fridge, on the right wall near the bottom is a small plastic grate. You should be able to pull this straight out from the side wall. There is a temperature sensor attached to the back of the grate. Unplug the sensor. (The fridge will then give you a very annoying error beep and display "EE" on the readout. Pushing the °F-°C button stopped the beeping.) This sensor will change resistance with temperature. (The lower the temperature, the higher the resistance) I was reading a resistance of about 3700 ohms at 43°F and 2460 ohms at 68°F. Throw in a rough assumption that the response is linear and it works out to almost 50ohms/degree. In order to 'trick' the fridge into cooling down more, you need to drop the resistance. I was aiming for about 6 degrees cooler. Assuming the resistance response was linear, 6 degrees cooler would give me about 4000 ohms from the sensor. By jumpering a 50000 ohm resistor (yes, 50K ohm) in parallel with the sensor, I should get about 6 degrees cooler. I did the soldering, plugged the sensor back in, and ended up about 8 degrees cooler. Two days so far, everything appears good and the beer is cold.

Short version:
Put a 50K ohm resistor in parallel with the temperature sensor behind the grate on the inside right hand wall.

The temperature read out will be inaccurate forever after though. But then, I just want cold beer, my wife wants cold water, and the kids want to play with the cool blue light. I don't care what the number on the readout is.

you will have to replace your thermostat of the fridge

you can find it near the light inside the unit

Same Guest as above posting this ... By the way, I have a FLSC238DS5 ... I spent 45 minutes on phone w/Frigidaire this afternoon (Phone#: 706-860-4110 Option 1 --> then Option 3). Didn't get anywhere. They say there are 3 solutions that should change it from C to F: 1) In between LED readouts for "Freezer Temp" and "Fresh Food Temp" there is a mode button that is hidden under the plate that you can press w/your finger OR 2) Hold "Fresh Food Temp" Up Arrow Key down, within 5 Seconds press "Freezer Temp" Up Arrow Key 3 times and it should change C to F or vice verse. Didn't work for me so she said 3rd option was to have a service tech come and diagnose. She said there would be a charge. I am not paying to have somebody come here to resolve this issue. That is when I asked her to escalate it to a supervisor which she did. Hopefully, I get a call back & a solution. Stay tuned ...

Is the compressor running? I don't know this unit, but know that if you are too warm that is the first thing to check. In reading about another unit that had a different problem, it was mentioned that there is a ciruit board. If it has relays on it then these are the most likely culprit. They are either not making contact or staying in contact too long... sometimes just tapping each relay usually a black plastic component will cause it to work intermittently..Not sure if you can get these but call the company help line at 1-800-263-2629.