This work presents a technique to improve the thermal performance of an R-32 air conditioner by using ultrasonic waves. Two 1-TR air conditioners — one with and one without 40 kHz/50 W ultrasonic generators — were tested under controlled conditions in a 3.6 m ×3.6 m ×2.5m room. The air temperature and humidity conditions entering the condenser and evaporator coils were controlled under 12 conditions to mimic the climate of Thailand. The testing results indicated that the average energy efficiency ratio (EER) of the modified ultrasonic R-32 air conditioner unit was 3.685 kWth/kWe and the normal R-32 unit without the ultrasonic generators was 3.375 kWth/kWe. The testing conditions also indicated that the cooling efficiency of the modified system could be increased by approximately 7.69%. Moreover, the convective heat transfer coefficient of the modified ultrasonic R-32 unit was approximately 17.36% higher than that of the normal R-32 unit without the ultrasonic generators because the ultrasonic waves could increase the turbulence in the refrigerant flow and decrease the condensed water at the fan coil unit. In terms of economic results, the payback period of the modified unit based on the climate of Thailand ranged from 0.8–1.2 y, leading to a savings in power consumption of approximately 400–620 kWh/y.