how can I fix a caradco sash that won't stay up on its own???
There are 2 counter balances on each sash. One or both of yours is broke or disconnected. Tilt the sash in and remove it from the frame and look at the balances. If you can't see the problem, remove a sash that works properly and compare them. Pay close attention to the removal process or another sash will have issues.
It could be a simple issue of the sash not being put back correctly and not engaging the balances.