| My 23 year old small simple (no defrost etc ) under-counter fridge (Bosch logixx Easy access Maxx Freedom Performance with sliding drawers) became more erratic over several months. If it was too warm (flashing LED's) there was a 'super' button to press to turn on the compressor continuously, but this no longer worked. |
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| First I replaced the 4uF start pump capacitor (£9) as it was out of spec (2.8uF), but that made no difference. Then I replaced the pump PTC thermistor relay (£13) as it was marked 25ohms and measured 45ohms. But even a new one measured 38ohm, so that made no difference. The pump coils' resistances seemed satisfactory (15 and 48 kohms). The fridge's thermostat (thermistors) also seemed OK (about 12 and15 kohms at 10C) and went up in resistance when the temperature went down. |
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| Thus by process of elimination, it was concluded that the fault must lie in the control board (the most expensive item up to £300 if you can find one). |
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| By chance, I found that when you disconnected the two thermistors (one inside the fridge and one outside I think) from the control board, the fridge starts working again but now in a timed mode. The compressor turned on for 15mins then off for 45 mins irrespective of the temperature, (25% duty cycle) ie if the control board appeared to think that the temperature sensors have failed, so it went into a 'safe mode' to protect the fridge contents. (I don't know if other fridges do this- I could find nothing on the internet). |
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| In winter this maked the fridge too cold at 0C, but by putting the fridge on a mains timer e.g. to turn off overnight, I could manage the temperature better. Conversely, if the fridge was too warm, due to lots of door openings, I could manually (or with a mains timer) turn it off and on again to start the cooling. |
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| This guide tells you how to fairly easily disconnect the temperature sensors (thermistors) so you can still use the fridge until a replacement/repair is possible. |
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| Later, I did a second repair to control the temperature more automatically by buying an STC1000 temperature controller (£8.50 on eBay). |
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| These simple external controllers are normally bought by people brewing beer that want to better control fridges, freezers etc. |
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| There was no need to empty the fridge for either of these repairs. |