1997 Jeep Cherokee defroster

You A/C cycles on and off when you run your defrost so that the humidity in the heated air is removed...
so if you are saying your A/C doesn't work, then that is probably why your defroster isn't working as well as you would like....
If you are saying you had/have a water leak under the dash, it may have affected the position andor operation of the blend door which mixes the A/C and Heated air circuit and routes it to your defroster...

Either way you probably need to to bring it to a shop.
If you feel you have the skills to tackle it yourself, you will need a Factory Service Manual at minimum to start, and then possibly some specialty tools to affect a repair.