Apple used a proprietary heat sensor on the hard drive of this machine. Use an OWC In-line Digital Thermal Sensor for iMac 2009-2010 Hard Drive Upgrade to cure this problem
[https://eshop.macsales.com/item/OWC/DIDIMACHDD09/?utm_source=google&utm_medium=cpc&utm_campaign=digitalthermalsensor&gclid=CJnvy-GMu9QCFQOtaQod7HECZA|OWC In-line Digital Thermal Sensor for iMac Late 2009 - Mid 2010 HDD or SSD Drive Upgrade]
Apple used a proprietary heat sensor on the hard drive of this machine. Use an OWC In-line Digital Thermal Sensor for iMac 2009-2010 Hard Drive Upgrade to cure this problem
https://eshop.macsales.com/item/OWC/DIDIMACHDD09/?utm_source=google&utm_medium=cpc&utm_campaign=digitalthermalsensor&gclid=CJnvy-GMu9QCFQOtaQod7HECZA