Went on a first last week, Customer had a restricted mortex coil nothing in heating or cooling so we pumped down and valved off system flushed line set with rx11 before coil install and washed out a black sticky goo. 410a split system heatpump any clues ? never seen this before. Called customer and advised changing outside unit and line set also after seeing this but he said he wanted to chance it with new coil and filter drier. Cant be good.