i have a 2010 keystone m fridege after pluged in for a week in outside temps of 50-60 deg temp 38-40 deg slider is at the top of fins. i cant imagine what will happen when the outside temp is 90 o...
What "fin" is the Thermistor on as you're looking at the inside of the frig?
AND
Think North ... UP (colder) .... South ... Down (Warmer)
To Test: Unplug the thermistor and let the fridge run essentially uncontrolled but check every few hours to avoid freezing, if it cools you have a faulty thermistor.