Hi i dont know the model of your unit but i believe it to be a single compressor type ,from what you say.some models have a fast freeze button which is sometimes pressed without noticing or deeper into the problem your thermostat is broken and because your freeze should be at least -22 degrees you wont notice it being -35 without a temp gauge.
please ring for further help or parts or call to repair 07855020738 ask for neil
neil
October 2009