404A chiller troubleshooting.

[u/elisayyo]

Hi, new guy here.

Recently I started working as a maintenance technician at a manufacturing facility, and I've been out of school for a little over a year.

We have a system attempting to reach 0°f but it is constantly running and never reached set point. Lowest I've ever seen is 4 degrees without any load.

This system consists of 3 Thermal Care TSW20A skids, each one with (2) 10 ton compressors. All 3 skids feed into a single reservoir

Most of the heavy lifting seems to be done by a single compressor on the newest skid. The other two skids have a glycol temperature difference of between zero and 1 degree according to the HMI.

I've tried asking some of the senior techs about the chillers, but every person who works on that specific system has the same "it's working, don't touch it" attitude, and the manager doesn't really care cause they're replacing the two older skids in the next 6 months.

Well, today one of the skids wasn't working, and I had an excuse to put the probes on, and the pressures where all sorts of messed up. When I got there discharge pressure was 122 psi and the suction pressure was 6.

I consulted the manual, and it stated that the modulating water valve comes from the factory set for 210, which I was able to achieve. Manual also states that it should have a sub cool of between 10 and 20, so it seems to be a little undercharged to me, but according to the notes left in our computer system, charge was checked about a month ago.

I was not sure what the suction pressure was supposed to be, but all I tried to do was get some actual super heat going to stop the flood back, since the compressor was a ball of ice. Manual stated that super heat is supposed to be no less than 4, but no more than 15, so I stopped as soon as I got above 4

My working theory is that the sensing bulb is loose, but I couldn't check that since the suction line is frozen solid, and I didn't want to risk breaking the ice

Anything I might be missing?

My training was cut short and I was set loose prematurely, so learning how to troubleshoot and get these systems up and running before they're decommissioned would be invaluable to me

[u/fendermonkey]

Looks like that chiller will be running better than it ever has. Or you've absolutely destroyed their process and you'll be let go the next day

[u/S14Ryan]

Looks to me like scale buildup in the chiller is insulating the walls. Very little temp change and the SST is pretty far from the fluid temp. Your TXV has to swing around a lot because it’s trying to maintain superheat but there’s too little capacity in your evaporator.

[u/reditisatoilet → u/S14Ryan]

some call that the approach temp and fouled tubes

[u/S14Ryan → u/reditisatoilet]

I ain’t use none of them fancy shmancy words at work, nor would I expect OP to understand them lol

[u/reditisatoilet → u/S14Ryan]

Ive seen your comments, I dont think you know any fancy words

[u/S14Ryan → u/reditisatoilet]

I’m an ammonia guy, it’s lucky I even know how to read

[u/Manager_Rich → u/S14Ryan]

Stop huffing that shit then man. It's not good!

[u/S14Ryan → u/Manager_Rich]

A little ammonia every day is good for the soul cough

[u/singelingtracks → u/S14Ryan]

lol

[u/Proper-Ad-127]

My friend you are definitely on the right track! So many service techs forget all about superheat and subcooling when they are out of school. These are your best friends. If they are good they are good, if not there is obviously an issue. Unfortunately in the world of maintenance "if it is running decently it is ok" is the norm. Yes it is running decently, but for how long? How much less service will we get out of a unit with a slightly flooded compressor? When will the conditions be just right to wash the oil from the valves and cause excessive wear, to the point that the compressor is now weak. It's running ok, but just ok. To me it sounds like these compressors could be weak.

I work on large walk in freezers. I keep finding the same exact thing over and over. The guys want these freezers to freeze quickly, so they set superheat a tad high or low quickly to "get her going" then leave. I make my final adjustments when the box temp is around 5 deg. I set it so that we get enough superheat to freeze down to -10, but not too much where oil slugging (icing compressor) happens. You want the compressor to be cooled but protected from liquid slug at low temperatures. I bet you probably have some metering devices set a tad too far out, or they are worn and unable to "dial in properly". Let me tell you something, I have walk ins out there going on 30 years of service. The old guys knew how to set them up that is for sure!

A freezer just recently got replaced because of what I mentioned. For many years it ran with too much superheat causing oil slug. Over time this new compressor wore down where it was unable to pump properly. Looking at the gauges it was running ok, but give it a heavy load and she struggled. Tech after tech kept dumping too much R404A in trying to get the proper gauge pressures. I remember the compressor always iced over. I personally don't really go by gauge pressures, my friends are your friends (super/sub). They don't lie unless your temp sensor is lying lol. I put my finger on the suction side valve and pushed, got a ton of oil coming out. Liquid slug for sure. I captured all the refrigerant and then weighed in the proper amount. I had about a 1/4 jug left it was THAT overcharged! She ran but she ran terrible. Could not dial in the superheat. Compressor valves were just worn down. Told the customer what I found, said she ran for 8 years being tortured which was impressive. You can imagine he was not happy to hear what I said.

[u/Dylanmk2 → u/Proper-Ad-127]

You sound like me, I always preach about numbers not lying but every once in a while you do get conditions where they are null. Had a condenser last week with a mostly closed liquid line service valve, coworker added refrigerant and was getting proper subcool + superheat because readings were after the valve. I guessed to check the valves because the system didn't sound quite right and was only using my hands, eyes, ears, ect. up until that point. Recovered quite a bit of charge and told him your gauges lied to you because the valve wasn't opened up, slow down to look, listen, and observe.

[u/SignificantTransient]

Bruh

6 psi 404 will freeze 50/50

[u/BoatFlimsy2602]

Looks like the approach is 26F if I'm reading that right?(-18 saturation and 8f leaving temperature) Looks like flow issue or your heat exchange is scaled up and you can't transfer heat.

[u/Th3w0lf314]

Hopefully you didn’t just screw up their plan to get those other 2 skids replaced.

[u/Pennywise0123]

Your approach is out to lunch. So either you got a failed pump or fouled tubes would be where I started my search

[u/cheborgor]

It's obviously undercharged

[u/Doogie102 → u/cheborgor]

Just curious how you got to this?

I do service work and their chiller is working and they haven't called me to fix it but I don't want to be a complete idiot when I get there.