Compound compressor again: I screwed up big time.

Have you ever been soooooo sure that you figure out an issue that you felt triumphant? Walking around like you owned the place and that the trial was over? After all that, only to find out you were entirely wrong and that you just replaced a whole large body compressor that probably never needed to be changed in the first place? Well, welcome to my world. People seemed to like my long write up on my compound compressor oil lockout issue. I kinda just wanted to leave it at that, but for the sake of telling the whole story I gotta admit that once the compressor was replaced (which happened after the first post), the lockouts kept happening...... The new compressor fluttered in the same way as the old compressor. I wanted to puke when I saw the alert in the morning that the compressor had locked out again. I was so sure I had been right. When I went in, sure enough the new compressor after about 15 minutes of running went to having fluttering oil pressure. I had literally replaced every component involved with oil prior to replacing the compressor. I had nothing left to replace.... Except the y10 valve. As I stated in my original write up, I had suspected the y10 valve could be an issue but it was just a guess. I had actually turned off the valve having suspected that maybe it was flooding the compressor. I reread the Carlyle book and sure enough it says in there “y10 required with r22”. I am running 407a so I assumed I was ok. Every old hand told me that y10 is only necessary for r22. EXCEPT, I have a weird situation on my low temp rack. Two of them actually have this issue. I have no idea why, but both racks have like 50-70 degrees of superheat. I'm under the impression that they have been like this for years. Until like 3 months ago, I didn't even know there was such a thing as too much superheat in a rack. I knew that most of my other racks had like 30 degrees of superheat, but I really didn't know that 70 is super high. So, because of this, I have always known every single compressor to run their y10 valves in the summer (going on my third year with racks). I just assumed this is normal. Maybe it is? Maybe y10 will activate with 407a even when you do have 30 degrees of superheat. I really don't have any frame of reference. All I know is that every other compressor at my store runs the y10 valve. My locking out compressor, however, was not... I checked the history and I could see that the discharge temp of the compressor was about 244 when it locked out. All the other compressors got only to 215. As it just so happened, the contractors that installed the compressor had mentioned they noticed the capillary tube was very rubbed on. Soooo, I decided to replace the y10 valve. For those of you who don't know, the y10 valve is also known as the “desuperheating valve”. It injects liquid into the interstage part of the compressor in order to cool it down before further compressing the gas and discharging it. So after replacing the valve, the moment of truth. I ran the compressor. One hour goes by.... Two go by. NO MORE LOCKOUTS! Every time previous, the compressor had locked out in 20 minutes or less. The discharge temps are now matching all the other compressors. The WHOLE TIME, the compressor had been locking out because of the damn y10 valve not activating. I don't know why this is. Maybe oil was losing viscosity because it was too hot? I have no idea. All I know is the problem went away! …... That is, until it locked out again. At this point I am wondering what god I had pissed off to deserve this humbling experience. I HAVE ADMITTED PUBLICLY THAT I'M A DOPE JUST LET ME GO! The next day after it locked out AGAIN. I looked at the fucker run ALLL DAY LONG. Literally. It ran for hours. Never locked out once. So I go into the history logs of the night it locked out. There is only one thing left I can see. At night, I noticed when the temperature dropped, the subcooler was shutting on and off. It ran solidly 100% during the day whenever I was there. The subcooler feeds into the interstage. The interstage pressure is controlled by the subcooler along with this other valve that maintains pressure in it (don't know the name of the valve. Maybe a CRO?). However, if the subcooler is turning on and off, the pressure in the interstage is gonna fluctuate. NOW, typically this wouldn't be a huge problem except for the fact that the oil reservoir pressure MUST be above interstage pressure in order to feed oil into the compressors. There is a check valve on the oil reservoir that if the oil reservoir pressure gets 20 pounds higher than the interstage, it will dump the pressure off. SO, if you got an interstage that suddenly goes from 65 down to say, 50, because your subcooler turned off, you'll most certainly cause the check valve (OCV) to blow off the extra pressure on the oil reservoir. Then if the subcooler suddenly turns back on and repressurizes the interstage, the oil reservoir probably gonna have no extra pressure to push the oil. It takes time for it to build again. For whatever reason, the oil float on compressor 3 is always the lowest(it is also the newest float). I turned the adjustment out a bit when it got put in but it was maybe only a quarter full compared to all the other ones that are half full. So what I did was, I adjusted the oil float all the way out so that more oil would feed into the compressor in theory, then I adjusted the subcooler to run a few degrees warmer and I forced it to stay on all night long regardless of what the liquid temperature got to. Then I waited.... For the first time in months, the compressor didn't lock out! It ran for hours at night with no problems. I had finally fixed this fucking problem. It's been running with no issues for about 3 nights now. Never have I had a problem like this in my career of 9 years. That might be a drop in the hat to some of you old timers, but still, it made me feel like a brain dead idiot. I was so confident of my prior triumph that I wrote a damn essay on it. I'm am happy that it is finally over though. Now to figure out why the hell I have so much superheat.... Majority of the txvs have 10 degrees of superheat or less but I haven't checked them all yet.... All the cases are at temp. Still seems weird. Temperature sensors on suction lines are accurate... Another problem for another day. https://preview.redd.it/9uchg3nwlgi51.jpg?width=4032&format=pjpg&auto=webp&s=78e2a3ce78b10982df78c722c73827ca25472161 submitted by /u/Hrrrrnnngggg [link] [comments]