Muhamad Asrul Affendi Mat Nor, Nurul Syahirah Mohd Nor, and Zulkurnain Hassan. “Automatic Pump Down Air Conditioning System for Refrigerant R22 Split Unit”. Politeknik & Kolej Komuniti Journal of Engineering and Technology, vol. 4, no. 1, Nov. 2019, pp. 23-30, https://app.mypolycc.edu.my/journal/index.php/PMJET/article/view/237.