• In this video, This Old House plumbing and heating expert Richard Trethewey shows how to prevent ice buildup from shutting down an air-conditioning system.

    Steps:
    1. Clean or replace the return-air filter to ensure it's not obstructing the flow of fresh air to the air conditioner.
    2. Confirm that the size of the air-conditioning unit can accommodate the diameter and number of cool-air ducts.
    3. Remove the metal access panel to expose the evaporator coil.
    4. Check the size of the outdoor condenser unit. Typically one ton of cooling is needed for every 500 to 600 square feet of living space.
    5. If the condenser is too big for the house, it can cause ice to form on the evaporator coils and shut down the system.
    6. Pump out and collect the refrigerant from the existing too-large condenser.
    7. Disconnect the old condenser and cart it away.
    8. Install a new appropriate-size condenser.
    9. Connect the new condenser to the existing electrical power supply and refrigerant lines.
    10. Remove the old evaporator coil and replace it with a new coil that matches the tonnage rating of the new condenser.
    11. Reconnect the ductwork and seal the new evaporator cabinet at top and bottom with sheet metal strips and foil tape.
    12. Braze new copper connections to the refrigerant lines.
    13. Insulate the suction line.
    14. Connect PVC pipe to the condensate drain and then attach the pipe to a pump.
    15. Run flexible tubing from the pump to a drain.
    16. If necessary, add refrigerant to the new system.
    17. Turn on the air conditioner to ensure it's operating properly.

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