York Types:
Got a weird one. Got an 1987 era R11 Centrifugal, 700 tons. Mod#YTJ3K3E3-CVC Ser#YHSM 276200 with a YTH-126 HJ code compressor.This chiller is used as the "summer" machine as they have a 300 ton machine that is the "winter" machine.
I will tell what I know has gone on but am still a little dark on details as I have only run a couple of calls on it. About 1 or 2 years ago, the chiller was overhauled by another reputable shop and sections of the condenser shell were cut to expose the discharge diffuser baffle as they had really loud noises in that section. The baffle was indeed cracked and the contractor rewelded the broken areas. Sometime after the overhaul, the noise returned.

I was out on this chiller last year and found it was low on gas and found A bad leak at the HPswitch captube which had been repaired before and was a result of vibration. Today when I had it started up to check the noise, I noted that the chiller was a bit low on gas and I found that this time a weld on a pipe going to the HP transducer on the shell itself has vibration cracks in it.
At a load of something below 50% FLA the noise coming from the condenser is absolutely unbearable. Above 50% the chiller sounds normal. I have seen plenty of Yorks growl at low loads and even had a YK that had very minimal noises on the same area of the condenser at low loads but NOTHING like this noise. On that YK I did inspect the diffuser and found no issues.
What do you guys say? What would cause that type of failure? Would it be due to running at very low loads?

Thanks for any input