\documentclass[border=3mm]{standalone}
\usepackage{luacoolprop}
\pgfplotsset{compat=1.18}
\pgfplotsset{auto node allow outside=true}
\begin{document}
\LCPPHDiagram[
  fluid=R134a,
  isotherm=true,
  isentrope=false,
  isochore=false,
  quality values={0,0.5,1},
  temperature values={0,40,80},
  labels=true,
  label placement=autonode,
  sloped labels=true,
  autonode candidates=31,
  label min pos=0.20,
  label max pos=0.80,
  axis options={
    auto node algorithm=repair,
    auto node bbox mode=axis-aligned,
    auto node failure mode=allow-minimal-overlap
  }
]
\end{document}