what is the function of the black ball connected to vacuum line behind pass side bumper

 

It provides vacuum for your air conditioning & heating system, as well as cruise control.

 

It is a vacuum reservoir. Like a tank of compressed air, but in reverse. It helps to stabilize the vacuum pressure available to your various vacuum powered controls even as the motor fluctuates in the amount of vacuum it is producing.

 

Here

 

Since I don't have a/c, heat or cruise control can I eliminate that whole section of the vacuum system? I'm trying to clean up the engine bay and remove what I don't need

 

As long as you don't mind only having defrost during the winter.

 

I have a 96 XJ and this canister is gone but the vacuum line plugged in its place right above wheel well inside the engine compartment on the passenger side. My defrost/vent/floor controls work when the motor is running, but I can't get the AC to fire the compressor. Jumped the relay and know the compressor works and even blows very slightly cool air. Tested the relay as well in my other XJ so I know it works... Also replaced the internal vent/heat/AC control module with no luck

What's the chances my AC issue is still that canister? If not that, where should I go with more diagnosing?

 

AC issue isn't the cannister.

 

Since you say the compressor is working, I would go with finding out if it has the correct amount of refrigerant in the system.

 

The smaller hard line on mine was broken. I can't wait to see what happens when I fix it. Expecting the heater vent ***** to function inside. Hoping it might lower the engine idle which is a little too fast.