As global temperatures continue to rise, the demand for air conditioning (AC) has surged, especially in hot–humid climates where efficiency is a major concern. Although humidity strongly influences AC performance, the specific effects of portable humidifiers on non-inverter split-unit systems remain underexplored. This study investigates the influence of a portable ultrasonic humidifier on the Coefficient of Performance (COP) and power consumption of a 9,700 BTU/h R-32 split-unit AC under typical Malaysian indoor conditions. Experiments were conducted in a sealed room using three humidification rates (100, 200, and 300 mL/hr) at two setpoints (20°C and 24°C), with continuous monitoring of temperature, relative humidity, and operating current. Results showed that at 20°C, COP decreased by up to 7% (≈3% on average across humidification rates), accompanied by a 6% rise in operating current, indicating higher dehumidification loads and compressor workload. Conversely, at 24°C, COP improved by up to 7% (≈3% on average), with a 13% reduction in current, as humidification helped optimize the balance between sensible and latent cooling loads. These findings demonstrate that humidification alters AC performance differently depending on the operating setpoint, highlighting the dual role of added moisture as both an efficiency burden at lower temperatures and a potential efficiency enhancer at higher temperatures. The study concludes that COP variations are closely linked to dehumidification requirements and recommends the integration of humidity-sensitive control strategies and adaptive algorithms in AC systems to optimize performance, reduce energy consumption, and enhance indoor comfort in humid environments.