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  1. #1
    Join Date
    Dec 2002
    Location
    Bozeman MT
    Posts
    37

    Question

    Thanks for taking the time to read this:

    Equipment:
    Carrier 30HR100 system circa 1968. This is a system with two circuits, 50 tons each. They share a tube in shell chiller barrel, though with separate tubes for each circuit. The chilling loop has glycol running through plastic piping integrated in the concrete of the rink. Each circuit has its own condensor barrel, also tube in shell. Both condensor barrels have glycol running through them to an external water to air heat exchanger activated by head pressures on each circuit. There are no liquid receivers on either circuit other than the condensor barrel itself. There are no high temp sensors on any of the condensors. Each circuit consists of 1 06E and 1 06D carlyle compressor. Both circuits using R-22. System has been running well this year since Oct. 21st with no problems.

    Situation:
    I was called in the AM after a cold front moved in (we went from 47 degrees the night before to 30 the next AM) to figure out why our chilling system at the local hockey rink was not running. When I got there, the floor chiller pump was running, the heat exchanger fans were on. The system was shut down on low pressure cutoff. I stopped and restarted the system to see what was happening and noticed immediately that low pressure side of circuit 2 was ~10#s and that the high pressure side was way low (like 40#s). I wanted to keep circuit 1 going since the ice was getting warm and the sun was coming up, so put the set points on circuit 2 warmer so they would shut off before the low pressure shut them off. Also took note of the fact that the Liquid line on circuit 2 was cold to the touch all the way pass the LL solenoid and drier. Circuit 1 was running fine, pressure were good.
    Started sniffing around with my detector to see where the leak was. Finally found that there was a major leak coming from the High pressure emergency discharge valve on the condensor #2. This is a Superior 3020A-400 valve, though I noticed the condensor barrel is only rated for 385 Psi!
    Started evacing the circuit from the TXV to the high pressure side of the compressors. I was drawing from the output side of the drier and noticed that there was a serious restriction somewhere that was causing the recovery machine to draw the circuit into vaccuum within a minute or so and it would take about 10 minutes for the 40#s to build back up again. Decided to try the opposite side of the condensor barrel thinking that there might be a plugged drier, same deal with that tap, very slow recovery. Let recovery machine run for 8 hours and finally got the system to stay in vaccuum for 4 hours after shutoff. Got about 12#s of refer from its full capacity of 68#s.

    Questions:
    Is it possible that a restriction in the condensor barrel caused this situation? There should be no way that the high pressure valve should blow unless the temp in the condensor barrel rose a bunch (like 350 degrees) or the high pressure valve is faulty and it blew. The valve I noticed was new in the last few years (everything else has nasty green paint, it was shiny brass) and I wonder if this same thing didn't happen before.
    Why would one circuit blow and not the other if temp of the glycol going to the heat exchanger was the same temp?
    Why would the valve only blow down to 40#s and then stop? I thought once they blow, that's it, they are wide open?
    I also noticed that it holds a vacuum, so the high pressure valve must have partially resealed...?
    If the pressure is the reason for the blow off, doesn't this mean that the condensor went hydro-static and that I potentially would have a broken rod in the compressor? The compressor ran fine for the 2 minutes that I started it up.

    Any help or ideas is appreciated. I am opening up the system tomorrow to check the drier filters and screens and check for an obstruction. Is there a quick way to test for an obstruction in the condersor barrel itself? Would pushing N2 from one end of the condensor to the other be a good test?

    Thanks,
    Scott

  2. #2

    Talking

    I'm wondering if this chiller set up you are describing has a high pressure switch for each circuit. And if so, are they set to trip below the rating of the relief valve as well as below the rating of the condenser.
    As far as sweeping nitrogen through refrigerant side of this liquid cooled condenser, I can't see any problem doing that. It may help determine if there is a restriction.
    Also,I'm interested in finding out if you find some kind of problem in the glycol circuit that cools this condenser.

  3. #3
    Hey Scott, I think you got three things happening there.

    Leak at the valve. For sure, for sure. Restriction at the filter drier.... sure sounds like it.

    #3, I dont think your pressure controls are set up properly.


    I may be wrong. But it would be the first time today for that.


    snicker, snicker ... but it's only one AM. ad the day is still young....


    Hope this helps.

    Replace that valve. Look in the Henry bok and see how you can "Y" that base fitting and install two blow valves, having only one in the circuit at a time. This enables you to isolate the bad valve and NOT have to recover all your refrigerant IF the valve should ever pop again.


    This shoudl be SOP on ALL equipment, but it aint!

    Considering what's at stake, look into it. It would sure save you time and money if it goes again. Like it has in the past.



  4. #4
    Join Date
    Dec 2002
    Location
    Bozeman MT
    Posts
    37
    Gentlemen,

    Thanks for your replies. After ordering parts, including a high pressure control and a new relief valve, I have put the machine back together. I did test the high pressure valve and as you had pointed out, it was bad. Hooked it up to a N2 regulator, ran it up to 350 Psi, no click and relay had not tripped yet. It was supposed to CO at 265 and CI at 185.

    Changed the filters while I was at it, nothing unusual, no metal parts, no excessive oil, everything looked fine... Blew N2 from one end of the condensor to the other, everything flowed just fine.

    My only other guess is that some water got into the system and collected and froze at the TXV and plugged the line?? Since this happened as the cold front moved in, the liquid line would have been much cooler than it was a few hours earlier.

    It's going to get warm in the next couple of days and I will watch it.

    Thanks again,
    Scott

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