Nissan Technical Advisor 9/23/2010Hi imran, you can buy a kit for checking this, as well as charging kits in any automotive store, a can w/ fluorescent refrigerant dye will help to pinpoint the location of the leak. The kit includes instructions. Also you can use an ac gauge to test the system for static pressure charge. Off the engine, attach the gauge to low pressure port and check the state of charge. The temperature normally should be around 50-80 psi.