I have a 07 impala LS 3.5L NON flex fuel.
My ac compressor wont budge its F.U.B.A.R.(its german

)
i want to fix it but i dont have the time to money to replace the compressor at this time.
SO
what belt size would i need for bypassing the compressor?
You can't re-route the belt on a 3.5L V6. The AC compressor is actually an idler that allows the belt to run the water pump in the opposite direction from the other accessories.
would it be dangerous to get a used compressor or is that TOO risky, how likely am I to pull a broken one out? Mine has NEVER worked in my car as long as I have owned it just flashing and I could hear the liquid sounded low, I assume that was probably part of the problem. its been sounding funky for days. sounding like a bad pully, but all the rest are free spinning and don't make that god awful sound.
The awful sound is probably the compressor clutch idler bearing failing. That part spins even if the compressor is seized. The idler pulley and bearing can be replaced independently from the compressor.
It's a fairly simple task as long as you can get access to the pulley end of the compressor.
You can probably pull the compressor loose from the mounts and swap the clutch without taking the AC hoses off the compressor.
If the compressor is seized you can still replace the clutch and bearing assembly and then re-install it as an idler pulley.
Honestly, if the AC system has had humid outdoor air in it for more than a few months it's FUBAR.
Here's why.
Outdoor air has Humidity and refrigerant oils will extract water from the air lickety-split... just like brake fluid. Water will make a weak acid when combined with all refrigerant oils. That cruddy oil will have to be removed from the system and the condition of the aluminum parts that were exposed to the corrosive crud will need to be assessed.
If you want to fix it...
IMHO The only way to reliably fix it would be to find a wrecked Impala 3.5L with an AC system that's still under pressure and buy the AC system off that rig lock stock and barrel to replace yours. The yard will properly evacuate the system before you or they pull the parts.
Once you get the parts you need to flush everything but the compressor out to get rid of any refrigerant oil, dump out the old compressor oil charge, buy a new drier, buy several ounces of Ester oil with UV dye, Re-fill the compressor with new dry oil (you may want to fill it and drain it once to flush out any crud), install the components, and sweep the system with nitrogen, helium, or argon. Welding gasses like those three are dry and not refrigerants so you will not get fined and put in jail for sweeping the air out of the system with them.
Most of us ******** have a tank of Argon for the welder.
I usually sweep the system out, vacuum it down and leave it overnight to test for leaks, and then I pressurize it with Argon welding gas til the LPCO trips to test the system for leaks again. The point is to get the humid air out of the system immediately after you close the last fitting.
DO NOT EVER SWEEP THE SYSTEM WITH REFRIGERANT. Some jackwagon will turn you in for venting refrigerant and the EPA will fine you and possibly put you in jail.
Once it's closed up and clear of humid outdoor air you can get a shop to vacuum it down or do it yourself and re-fill it...
Most rigs aren't remotely worth the expense to fix an AC system that's been left open for too long.