Does the window crank turn as the window going down? I believe there is a spring that is supposed to provide some counterforce to the weight of the glass - might be something to check.
-- Edited by MC on Wednesday 12th of June 2019 11:10:32 AM
counterbalance spring must be broken or detached. Be careful btw, that spring can be nasty to your fingers as in scissors if your finger gets in the wrong place