Arrived to remedy an inoperable air conditioning system. Upon arrival found that the system is low on r 22 refrigerant. Due to the lack of that refrigerant did not propose any repairs. With homeowners approval reached out to a supervisor to provide information on a more efficient system. Continued diagnostic of the air conditioning system and furnace. Found that the blower wheel is heavily coated in debris. Also, found that the heat exchanger is damaged and has been leaking carbon monoxide into the home. Upon arrival of the supervisor went to inspect the unit in the other half of the duplex. The furnace on that side shares the same story. The heat exchanger is showing signs of age. Cracks and rust beginning to form in the steel and is on the verge of failure. Supervisor spoke with homeowner about replacement solutions. Two new systems for each side of the duplex are scheduled to be installed tomorrow.