In winter when the heat pump (air con) inside unit heats the inside of the house the outside unit blows cold air across the outside wall and window of a bedroom. There is black mould spotting on the weatherboard outside wall and on the curtains inside the window. Today I will adjust the outside unit at an angle so the cold exhaust blows away from the window. I discovered the mould when I was painting the window frame. I am certain that the influence of cold air in winter when heat is needed in the house gets black mould going with health problems for residents. I will try a 3% spray of hydrogen peroxide on the curtain liner on a small trial patch to see how that works. HHOO is a bleach.