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Sub-Zero 550 fan will not shut off and refrigerator compressor will not shut off despite being cold


Premium Member
May 23, 2023
Model Number
More than 10 years
I have a Sub-Zero 550 from 1990 that I inherited with a house purchase that was not getting cold. I found the condenser motor fan was broken off and the motor was all gunked up so it would not spin. I replaced it with a working parted out oem Sub-zero 4200740 with the same specifications that were in the original (2.3W 0.15A 115V 1300RPM). I also steam cleaned all the dust and gunk from all the tubing and between the fins. I replaced all the dried out / cracked plumbers putty and removed and replaced all the silicone waterproofing. I set the unit to the recommended temp settings of 4 and 6 to target 0 degrees for the freezer and 38 degrees for the fridge. After running overnight the problem I am having is the compressors and condenser fan continue to run nonstop but the freezer is at -18 degrees and the refrigerator is at 30 degrees. I tried lowering the temp settings to 3 and 5 but that did not help as the temperature changed to 4 degrees for freezer and 32 degrees for fridge but still did not cause the compressors or condenser fan to kick off. The freezer compressors is about 121 degrees and the fridge compressor is about 104 degrees. Door are sealing tightly all the way around and it completely level front to back and side to side. Circulation is good as grill cover is warm on compressor side but cool on the condenser side. The only way I could get compressors to stop is turning dials it off positions but the fan continues to run and obviously the fridge and freezer stop cooling. Any suggestions on what I should be looking at?
Depending on ser# the cond fan will run 100% of the time. Frz- is evap fan running with upper basket pushed back. Ref- what does evap frost pattern look like
Based on your feedback I found this reference indicating that the fan for my serial number (an early 550) does run all the time.

Yes the freezer basket is in all the way so that the light turns off.

I have no frost patterns or condensation on the back wall (I haven’t removed it to see the evaporator coil) and after filling it with food last night it has been maintaining a constant 0 degrees and 36 degrees in various locations with temp settings at 4.5 and 6.5.

Based on all that it sounds like it is operating as expected. Fell free to let me know if that sounds about right.

Appreciate your help.
Ok thank you. I will dissemble this weekend to look at the ref evap and freezer fan. Thanks.
You should be able to hear the frz fan by pushing back the basket if the compressor is running. In the ref by removing the shelves, light cover and fan cover you can tilt panel forward to see the evap. Careful as the cap tube for the frz is tight. See how many cap tubes are on the ref control.
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