Responded to a no-heat call for an 80's era furnace blowing cold air. Upon arrival, system was locked out due to overheating with supply air temperatures approaching 150°. Diagnosed severely restricted airflow with almost 1" WC static pressure on return side and minimal static on supply side. Found only two functional returns throughout home, multiple closed vents, and heavy dust accumulation in ductwork. Reset system, opened basement vents, verified all supplies were open, and inspected burners (found crusty). Noted system using cooling wire on blower for heating due to furnace running hot. Verified proper gas pressure, correct orifice, and functioning blower capacitor.
