Samsung s-rs2026cvw side by side f/f question

Hi all. I recently had a problem with the fridge half of this model freezing at the bottom. I was able to cure this with the help of these very pages (thank you to all!). However, during the course of the problem, I was using an old type non-digital thermometer to check temperature. Too coincidentally for my liking, the day I got rid of the ice in the fridge half, the freezer started behaving in a peculiar fashion. The temperature display on the front would fluctuate between -8 and -18 (which it was set at). I put the old thermometer in the freezer to monitor it, and after a couple of days, I noticed that it seemed to settle down to -20 (new setting)steadily. I left the old thermometer in it as a check and what seems to happen is that althought the panel displays -20 all the time, the actual temperature varies between -10 and -20 on a cycle of some hours. What I was wondering is, is this the normal chill/defrost cycle working or is it knackered!? And did I shock it with my steam cleaner treatment of the fridge half? And if the fridge starts to form ice again, what can I do? Hope you can help (again)