Chosen Solution
Thats the problem as SMC is seeing the fan has failed so its pushing the other fans to make sure your system doesn’t cook. While a SSD runs much cooler than a older 3.5” HDD you’ll still need to replace the fan iMac Intel 27" (Late 2009-Mid 2011) Hard Drive Fan. We don’t have a direct guide to get to it as its under the logic board. Update (10/20/2021) OK, did you install the sensor as shown in Step 19 iMac Intel 27" EMC 2390 Hard Drive Replacement Also check your connections to the logic board
