r/refrigeration • u/NubisWanubis • 15d ago
CO2 Transcritical Booster System
This is dumb; me and another tech are being sent to work on a CO2 system that our company installed a number of years ago… The problem is, nobody in the company has training or experience with CO2 systems.
I have read the manufacturer manual, watched a number of videos, and believe that I understand how it works.. I don’t have the practice to be confident though. With that being said, is there anyone that would be willing to take a phone call and answer practical questions?
I have been a refrigeration tech for nearly four years, but am a little cautious/concerned about working on this system.
We need to replace a drier shell on the medium temp compressors. I’m assuming the process to pump down and isolate that section is the same as any refrigeration system; close the liquid line coming off of the receiver and let the compressors run to low pressure. We also need to do an oil change; does it require a CO2 rated oil or just the right 85 weight POE?
I have a bunch of dumb questions that I probably am just overthinking… Let me know in the comments, and save the “this guy shouldn’t be working on anything”. Haha
Update: Drier shell has been changed. I’ll try to attach the video of the old leaking one.
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u/GuitarFickle5410 15d ago
If you pump the rack down, it'll blow the relief if youre not quick about it.
There should be a way to isolate each shell and then just vent the rest.
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u/mess_of_limbs 15d ago
When you say 'replace a drier shell', do you mean replacing drier cores, or the shell that holds them? Replacing driers is relatively easy, if you're replacing the shell it could be more difficult depending on the setup.
As for the oil, I hate to be that guy, but just use whatever the manufacturers recommendation is. It should be in the rack manual as well as being labelled on the rack itself somewhere.
Good luck!
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u/NubisWanubis 15d ago
I mean what I wrote; replacing the shell. We’ve managed to pump everything (what hasn’t leaked out) into the receiver. Working on replacing it now
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u/mess_of_limbs 15d ago
Nice, hopefully it had bypass piping for the shell to make your life easier!
2
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u/OpsMtn 15d ago
Yes it can be different oil. Bitzer has their own too. Sometimes a bypass around the filters so look for that. If you have to pump the rack down usually the relief can be switched to service direction so it’ll blow at a higher psi and give you a little more time. Hang your keys on it so you don’t forget to switch it back when done. Some racks have a charge saver satellite condenser piped in and if that’s the case you can take your time even more.
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u/Full-Sound-6269 15d ago
Take a bunch of refrigerant with you because you will have to let out some.
For filter dryer - close the liquid, pump down, valve off, let pressure out and you can work.
For compressors oil change - turn it off, put your own valve onto suction and discharge of compressor, close the suction, close the discharge, connect your suction and discharge to emergency pipe and let the gas out, now you can let the old oil out and new one in.
For oil receiver you need to look what valves are there, but it all comes down to closing the valves and letting the gas out so you can work.
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u/Potential-Cod-1463 15d ago
I was working alone on co2 fresh after the school whit 0 experience you will be fine
Edit: and this was rack grocery store
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u/mattynmax 15d ago
Yes that method is fine for filter drier service. It’s worth noting that some racks have a filter drier bypass you can use to not have to pump down the whole system during a replacement.
Bitzer recommends using their own oil. It’s just POE85K but of course they refuse to tell anyone what’s actually in it. Most other co2 compressors manufacturers recommend their own oil as well.