Air-source heat pumps (ASHPs) suffer from significant efficiency degradation under low-temperature, high-humidity conditions due to evaporator frosting. To address this, superhydrophobic coatings were applied to the aluminum fins of an ASHP evaporator to delay frost formation and accelerate defrosting. This study evaluates the frosting/defrosting performance of superhydrophobic coatings under real-world operating conditions using commercially residential ASHP units. Three configurations were tested: original hydrophilic fins with default defrost strategy, superhydrophobic-coated fins with default strategy, and superhydrophobic-coated fins with a modified COP-based defrost strategy. Results demonstrate that the superhydrophobic coating alone extended the first defrost interval to 323% of the hydrophilic baseline, reduced average defrost time by 61.1% and defrost energy consumption 60.7% over 8-h operation. After defrosting, residual moisture was significantly minimized on coated surfaces, and frost layer detachment during defrosting contributed to accelerating melting. Implementing the COP-based strategy on coated fins further enhanced system efficiency, increasing the 8-h average COP by 2.3% compared to the default strategy. This integrated approach—combining superhydrophobic coatings with optimized defrost strategy—enables sustained high-efficiency ASHP operation in cold, humid climates while ensuring user comfort.