fast knocking noise when ac is on

[bigred93explrer]

engine runs smoothly and sounds normal until i turn my a/c on and then i get a fast knocking noise....is this a normal noise i should be hearing or is it a problem

 

[91EX4x4]

I would say that it might be a problem. Is itcoming from the A/C compressor/clutch? I know my compressor locked up all of a sudden and I tried to turn my A/C on and it started making weird noises and smeeled like something was burning(that would be my compressor clutch ). I kept driving it and a few days later the clutch decided to cycle on and it off the pulley! I had to get a junkyard A/C compressor that didn't work so I could use it to let the pulley freewheel to get home. Good Luck