The working fluid that carries heat between the indoor and outdoor coils. Modern systems use R-410A or the newer low-GWP R-454B; older refrigerants are being phased out, which raises recharge costs on aging systems.
Around Baltimore, Annapolis, and the DC metro, cooling decisions revolve around humid Mid-Atlantic summers, correct sizing for row houses and older homes, SEER2 efficiency, and whether a repair or a planned replacement is the smarter long-term spend.