I purchased a new Bosch fridge freezer and it is around 1 week old. Within the first day of turning it on there has been a build up of a thin layer of frost on the interior back wall (just in the middle, never at the top or bottom). Sometimes it melts and leaves droplets of water and then sometimes it becomes ice. This occurs every day.

I had a Bosch engineer look at it but they claimed that this is normal and all fridges work in this way today. But I'm a bit skeptical.

Any advice would be appreciated. Thank you

⟐ Answered August 18, 2023 at 15:49 MST

I recently checked all the refrigerator components (PTC relay, start capacitors, pump windings, thermistor response (2 off), and some control board component (capacitors, triac, diode), but couldn't find any signifiant fault (I did change the 4uF start capacitor as it had dropped to 2.9uF (no difference) and re-soldered one iffy joint (no difference)

By chance I found the pump would run and cool if I disconnected the two NTC thermistors (thermostats) with a starting wattage of about 60W quickly dropping to about 40W, as the start relay cut out.

But after exactly (to 10 secs) and reproducibly 15 mins, the pump stopped again. Then it started again exactly 45min later and so continued in this safe mode at about +3C, I guess to protect the fridge contents. Do other fridges have this feature? why are there two thermistors? could I use a universal fridge thermistor?

This is not a long term solution as the fridge will need a longer cooling time in summer or in heavy use and the only manual over-ride is to turn the fridge off and on again when it stops cooling to restart the cycle. (you can't change the on/off ratio by adjusting the temperature on the front panel)

Any ideas what else I can do, given that most of the parts are obsolete and no service manual is available online.

⟐ Commented January 22, 2025 at 9:33 MST