Objective: Flush out any harmful foreign substance including Compressor oil that might remain inside the Evaporator coil. Procedure: 1. Open Expansion valve with full turns clockwise and leave it open. 2. Connect Nitrogen to the service valve attached on high pressure side tube line. 3. Get a piece of clean tissue paper and place it close to the output port of low pressure side tube line. 4. Open Nitrogen gauge and allow to blow for a while. (* You can hear sound of blow from the video footage above.) 5. Allow Nitrogen to keep blow and in the meantime block the output port of low pressure side tube line using your thumb and check the Nitrogen gauge to see if the its pressure is high enough to flush out whole refrigeration cycle system. (* In the above video footage the Nitrogen gauge is read about 270psi.) 6. Now let go of your thumb. (* You can hear sound of pop out from the output port and there might be Compressor oil or any foreign substance come along.) 7. Go back to STEP 5 if you consider there may be more of Compressor oil or foreign substance remain inside the Evaporator coil.