Furnace runs but some rooms are much colder than others; airflow seems weak at distant vents.

Safety: Turn off power before opening duct connections.

Steps:

• Check dampers: Ensure manual dampers in the ductwork are fully open to cold rooms.
• Inspect accessible ducts: Look for crushed, disconnected, or leaking duct sections and seal with appropriate duct tape or mastic.
• Clean internal filter: If your Cointra furnace has an internal filter, remove and clean or replace it.

Professional service: A HVAC technician can perform airflow measurements and rebalance the system if needed.