Tested system not heating for the whole home. Found pan full of water from the air condition. System being low on refrigerant due to a leak that is likely in the evaporator coil. Remove the safety from the pan to test the heat and inspected the heat exchanger. Found cracks in the heat exchanger along with performed a carbon monoxide test from the vents that had a max of 4 ppm. Inform the customer that the heat is not safe to run at this time due to the cracks and the heating exchanger. Based on our findings today, it might be time to think about getting a brand new system.