if you're given just the temperature and internal energy of R134A how do you determine the phase of the substance? If I was given the pressure instead of internal energy then i would just look in my tables to see if the pressure is above or below the saturated pressure and i would then know whether it's subcooled or superheated. i don't know where the substance is with respect to the saturated liquid curve if all I have is the enthalpy. is enthalpy represented in any way on a pv or pt graph? Also, when substances are subcooled they would always have to be a mixture of vapour and liquid wouldn't they since when you move below the saturated r134a or water curve you move slightly closer to the vapour side of the parabola and vice versa.