To　improve　the　defrosting　accuracy　and　the　energy　efficiency　of　the　air-source　heat　pump　(ASHP)　under　frosting　and　defrosting　conditions,　a　novel　Temperature-Humidity-Time　(T-H-T)　defrosting　control　method,　based　on　a　frosting　map　for　the　ASHP　unit,　is　proposed　in　this　paper.　A　field　test　was　conducted　for　two　heating　seasons,　to　verify　the　feasibility　and　applicability　of　the　T-H-T　method.　The　advantages　of　the　T-H-T　method,　compared　to　the　conventional　Temperature-Time　(T-T)　defrosting　control　method,　are　presented.　In　total,　eight　cases　are　shown　in　this　paper.　Cases　1　to　4　were　chosen　to　reveal　the　T-H-T　performance　under　different　frosting　conditions.　It　was　found　that　no　matter　what　kind　of　frosting　conditions,　defrosting　was　always　initiated　in　a　similar　situation:　similar　to　90%　of　the　outdoor　coil　surface　was　covered　by　frost;　the　temperature　difference　between　the　compressor　suction　and　discharge　increased　by　similar　to　20%;　and　the　heating　capacity　decreased　by　similar　to　30%.　These　results　indicate　that　the　T-H-T　method　can　make　an　accurate　decision　under　different　frosting　conditions.　Cases　5a,　5b　and　Cases　6a,　6b　were　two　groups　of　cases　to　compare　the　advantages　of　the　T-H-T　method　against　the　conventional　T-T　method.　Cases　5a　and　5b　were　chosen　for　the　non-frosting　condition.　It　was　found　that　the　T-T　method　initiated　the　defrosting　operation　31　times　within　24　h.　However,　none　of　the　defrosting　operations　was　conducted　for　the　T-H-T　method.　Cases　6a　and　6b　were　chosen　to　compare　these　two　methods　under　consecutive　and　variable　frosting　conditions.　For　the　T-T　method,　63%　of　the　defrosting　processes　were　found　to　be　executed　under　conditions　where　defrosting　was　not　necessary.　However,　for　the　T-H-T　method,　all　the　defrosting　controls　were　found　to　be　accurate　and　reasonable.　These　results　indicated　that　the　novel　T-H-T　method　is　suitable　for　the　defrosting　control　of　the　ASHP,　and　has　a　more　competitive　performance　than　the　conventional　T-T　method.　(C)　2015　Elsevier　Ltd　and　IIR.　All　rights　reserved.