Ok When the car is idling or coming to a stop and the a/c is on the inside dash vibrates and it gets really bad when the fan comes on.

Also when im driving with the A/C on ill hear this loud screetching sound like fingernails on a chalk board coming from the car, the higher fan speed the louder it gets and longer it lasts. I recently put an A/C belt on the car to get the ac going and it just goes to the crank , compressor, and tensioner. Could this be a culprit. Its really embarrassing.

 

if its lose it will squeal if its to tight it will scream...and the is fan bolted up?

 

the fan is bolted up.

Ive noticed a lag in performance evan with the A/C off since i put the belt on.

So should i tighten it or loosen it?

Could bad grounds cause any of this

 

Make sure the A/C belt is tensioned properly. Sounds like it is too loose.

 

Bearing inside the ac compressor could be bad.

 

yeah if the compressor is shot it's going to put a massive load on that belt making it squeel even if it is the correct tension. that also puts hella strain on your engine, making the idle drop to shaking speeds (500rpm-)
Get a new compressor