Windshields

Hello, I have now for almost 14 days my send V70 I Bj. 1998 everything tiptop in shot and runs like a one….. …..however: With me the windows affect as soon as I have turned on the heater. There is only a little bit of turning up already the windshield runs on. I can also not get this under control when I turn on the climate and put on disc ventilation (so top position at the ventilation) After some drive all the windows have started. This is prevented only when the climate is constantly on in disc ventilation mode. Is only asscold in winter. Air conditioning and heating function otherwise great. Someone’s idea? Otherwise I will have the ventilation cables checked! Thanks and fine laaanges weekend!