Filter, airflow, capacitor, charge, ducts: the sequence that finds the cause without buying parts on guesses.
Diagnosis, repairs, and full systems in published ranges, and the repair versus replace arithmetic.
What clicks, what glows, what proves flame, and the safety lines that come before any repair.
The 5,000 rule, refrigerant reality, and the duct question that changes replacement quotes.
Less oxygen in every cubic foot changes how Englewood furnaces must be set up, measured, and sold. Why the combustion reading is this market's signature document.