PAGs　are　now　being　considered　as　the　lubricating　oil　in　R290　room　air　conditioners　(RAC)　owing　to　their　low　pour　points　and　low　solubility　with　R290.　However,　little　research　concerning　the　flow　characteristics　and　migration　behavior　of　the　partly　miscible　PAG　in　the　R290　RAC　during　dynamics　processes　has　been　reported.　In　this　study,　visual　observation　was　conducted　to　analyze　the　migration　of　oil　during　startup　and　defrosting　process.　Results　show　that,　during　startup　process,　though　excessive　oil　was　discharged　from　saturated　compressor,　annular　oil　film　and　oil　crystal　was　observed　at　EEV　outlet,　the　oil　can　finally　return　to　compressor　in　the　form　of　linear　flow　when　system　parameters　gradually　reached　equilibrium,　even　though　at　extremely　low　ambient　temperature.　During　defrosting　processes,　the　separated　oil　droplets　were　found　at　the　EEV　inlet　when　the　RAC　switched　from　heating　to　defrosting,　or　from　defrosting　to　re-heating　mode.　The　observed　adhesion　behavior　of　these　oil　droplets　near　EEV　increased　the　potential　risk　of　oil　blockage.　The　larger　EEV　opening　was　supposed　to　be　used　during　this　period　to　increase　the　reliability　of　RAC.　©　2023　Elsevier　Ltd　and　IIR