I have an 89 Accord LXI that I recently replaced the engine and transmission. Now when I turn on the A/C the engine rattles so bad that it seems like it will shake itself apart. It didn't have this problem with the old engine and I have replaced the A/C compressor 3 times but it doesn't fix the problem. Any help is appreciated.

 

maybe it could be your engine mounts maybe the extra force on the engine when the compressor is on is causing it to shake rattle and roll.