Sometimes when my truck sits for a day or so & then I drive it & turn on AC for first time the compressor makes a bit of a sudden clunk or big vibration when it kicks in. Seems to happen little more when it's real hot. Is this something that I should be concerned about and is there anything that is supposed to be used on the compressor to oil it or maintain it?

 

mine also does this cause i had it charged and they added stop leak since they could not find the leak, i am assuming it is the lowest point so it all settles there, or my compressor is the leak

 

I asked around at the auto shops a little, and they recommended using some of the freon in small cans with ester oil in it. they said it could help if the compressor needed to be oiled & I've never put any oil in mine......I got a can and will try it out. I will post if it seems to fix the problem......