The HVAC Technician Troubleshooting 2 Pack comes with 2 charts. One chart walks you through step by step, the troubleshooting process of diagnosing high efficiency furnaces. Simply set the chart to step 1 and follow the steps until you have diagnosed the failure. The other chart is for troubleshooting Air Conditioning and Refrigeration systems. Set the chart at the equipment system and read the probable causes to investigate. These charts are great for the beginning technician or for an experienced tech that needs to sharpen their skills.