The whirlpool freezer is an upright AFB433/G model. On fast freeze it just freezes everything solid, but if I switch off the fast freeze the temperature just keeps dropping even with the setting at maximum and the warning light for the temperature does not come on and food starts defrosting.

Gerald O'Brien, May 2004

you need to replace the thermostat.
when you switch to "fast freeze" you are by-passing the thermostat, thats why everything is freezing solid.
if left on "fast freeze" for to long a time it is very likely to over heat and burn out the compressor-----also a possible fire risk.

keith mcpherson, January 2006