Bosch thermal switch replace
Hello,
I have a Bosch KGU57990/03 fridge and the defrost thermal fuse/thermal switch has failed.
The original complete part is:
Heater-defrost, thermal fuse included — Bosch reference 00266836
The heating element itself is working correctly, so I would prefer to replace only the thermal fuse instead of buying the complete heater assembly, which is quite expensive.
The markings on the original thermal switch appear to be:
43F / 77158
Does anyone know the correct opening/cut-off temperature and reset temperature for this thermal switch, or a compatible replacement reference?
I would also appreciate confirmation of whether it is a resettable thermal switch or a one-shot thermal fuse.
Thank you.
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Ai states this thermal fuse does not reset when rated temperature is exceeded. My guess is the '43f' in the oem number may be the rating for 43F/6.1C, opening at 43F. A simple test; place thermal fuse/heating element in freezer until it stabilizes, measure resistance across this fuse. A separate thermister measures evaporator temps as the main temperature sensor to determine when to shut off the heater. There are replacement thermal fuses but not Bosch. If you choose to risk possible fire hazard and electrocution by attempting repairs instead of replacing the entire assembly, there are thermal fuses but you'll have to determine temperature and wattage rating as well as electro welding wiring to ensure correct joining of heater and thermal fuse and water proofing joints. Other manufacturers allow thermal fuse replacement. Apparently Bosch doesn't. Safety must be considered relative to diy repairs.
door F Dryer
Thank you for the detailed reply and for highlighting the safety concerns.
I am still unsure whether this is really a non-resettable thermal fuse. My assumption is that below 43°F the contact is closed and above 43°F it opens, with a certain hysteresis before resetting. If it permanently opened at 43°F / 6.1°C, it would already fail at room temperature, so “43F” may not be a one-shot cut-off rating.
On similar Whirlpool systems, the opening and reset temperatures are clearly specified, but I cannot find this information for the Bosch part.
I work in electronics and understand the precautions required, especially in an area exposed to ice and condensation.
Do you know any compatible thermal switch or fuse reference?
door Bruno Matos
I haven't researched thermal temperature fuses (the hint that its not resettabIe) but familiar with different types. Older refrigerators used a current/thermal switch wired into the starting coil of a compressor. If rated current is exceeded during startup, this safety switch (bimetallic) opens and will not allow compressor operation. A rupture releasing refrigerant, short in motor starting or run coil would trigger this switch, preventing drawing so much current that the fused outlet would trip. After a few seconds pass when the bimetallic element cooled down, it would close and starting current allowed. These old refrigerators can be heard as the switch would have a loud click with zero sounds from the compressor.
A search for specs from other thermal fuses wired in series with heaters used as defrosters can help you determine if 43F is a good value. Electronic parts distributors like Mouser and Digikey may have various types of thermal fuses with specs.
door F Dryer