The　development　of　a　new　frosting　map　for　air-source　heat　pumps　(ASHPs)　based　on　a　temperature-humidity　chart　is　reported　in　this　paper.　Through　a　parametric　analysis,　two　boundary　lines　(a　condensing　line　and　a　frosting　line)　were　obtained,　dividing　the　map　into　three　regions:　a　non-frosting　region,　a　condensing　region　and　a　frosting　region.　Using　the　simulation　results　from　a　generalized　numerical　model　of　frost　growth,　the　frosting　region　was　further　divided　into　three　indicative　zones　representing　different　frosting　levels:　a　severe　frosting　zone,　a　moderate　frosting　zone　(I,　II)　and　a　mild　frosting　zone　(I,　II).　Lab　and　field　tests　were　conducted　in　order　to　verify　the　correctness　of　the　zoning　and　to　obtain　indicative　defrosting　intervals　for　ASHPs　operated　at　different　zones.　Based　on　the　test　results　and　using　the　developed　map,　reference　defrosting　intervals　were　suggested　for　different　frosting　zones,　and　they　can　be　used　in　conjunction　with　a　conventional　defrosting　control　method　to　avoid　potential　mal-defrosting.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.