have some good properties, relative stable, non-toxic, and non-flammable. R-134a is a class of HFC (Hydro Fluoro Carbon) type refrigerants that contains no Chlor or compounds that can damage the ozone layer.This research investigates evaporation’s heat transfer coefficient of refrigerant R-134a in a smooth vertical pipe withsteam quality variation. The value of the evaporation heat transfer coefficient is one of the important properties in the design of evaporator. The method used in this research is the experiment using the test equipment in the form of a series of components of modified vapor compression system. Test section is made of copper pipe. Copper pipe diameter 16,60 mm deep, outer diameter 18,60 mm with length 1,25 m. Pralon pipe for outer length 80 cm, nominal diameter 2 inch and isolated using foam, aluminium foil and plastered rubber vapor quality varied from steam quality 0,19 to 0,74 set with electric heater. The refrigerant is also varied by adjusting the frequency of the inverter (14, 16, 18, 20, and 22 Hz). The research results that with the increase of steam quality, the evaporation heat transfer coefficient is increasing. The evaporation heat transfer coefficient also increases as the refrigerant mass flow rate increases. The highest evaporation heat transfer coefficient of 2484,53 W/m2.K at steam quality 0,74 and at 22 Hz inverter frequency yielded 0,0107089 kg/s refrigerant mass flow rate.