Paying for gas top-ups without a leak test
Refrigerant does not deplete in a sealed system, so a top-up without finding the leak is renting the same repair annually. Insist on a leak test and a written note of gas type and quantity added. Two top-ups in two years is proof of a leak nobody looked for.
Washing filters but never the coil or blower
Filters catch the coarse dust; the fine shamal fraction sails through and mats onto the wet coil and blower wheel, where a household rinse cannot reach. If airflow stays weak and bills keep climbing despite clean filters, the machinery behind them is the problem, and it needs a chemical wash.
Closing vents in unused rooms to save energy
On a ducted system, closed supply vents raise static pressure in the ductwork rather than saving money: airflow across the coil drops, icing risk rises, and the blower strains. If a room genuinely never needs cooling, the right answer is a damper adjustment at the unit or a zoning setup, not a shut grille.