Furnace repair downstairs system. Find 26 year old carrier system. Find pilot light out. Check and find gas valve not operating properly, burner not burning properly and system calibration off. Furnace overheating with 72 degrees delta T. Find heat exchanger rusted and high concern CO 70 PPM while system operating. Evaporator coil badly rusted and have some molds in supply plenum. System operating now but will fail again. Find upstairs furnace operating but dangerous CO level a 2700PPM. System no longer safe to operate. Turn system off. Find furnace heat exchanger badly rusted. Due to poor conditions and not safe to operate. System need to be upgraded to meet code and EPA Regulations. Give customer estimate to upgrade systems and pictures on conditions of system.