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  1. #1
    Join Date
    Jun 2012
    Location
    West Virginia
    Posts
    22

    AGS300B flow with plugged tubes?

    both circuits tripping on low evaporator refrigerant pressure and I have been told that 5 tubes have been plugged, checked glycol concentration and it is 38% propolyne. going back tom. to start diggin. just wondering how do I find out the flow with added press drop caused by plugged tubes. Also there are no guages but there are 2 drains on bottom end bell but what are the chances they are ew and lw? any suggestions?

  2. #2
    Join Date
    Jan 2011
    Posts
    1,223
    I'm not familiar with the machine you are working on, but unless it's a very small machine with less than 50 tubes then 5 plugged tubes isn't your problem. Three things can cause low pressure in a chiller...low flow, short of refrigerant or dirty tubes.

    Are there any ports on the entering and leaving chilled liquid piping?

    How long have the tubes been plugged?

  3. #3
    Join Date
    Jun 2012
    Location
    West Virginia
    Posts
    22
    I did find a plug in the leaving chilled water piping but everything else is insulated. I saw on paper that they checked the flow and pressure drop at startup which was 7 years ago but I dont know how because there are no gauges. tubes were plugged in 08. I may have to install gauges but I am not sure how the plugged tubes will affect my press drop.

  4. #4
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,340
    That's a air cooled machine...right. So the only tube bundle you have is the evap.....right. That evap is DX.......right. So the tubes are on the refer side.....and they are plugged?

  5. #5
    Join Date
    Jun 2012
    Location
    West Virginia
    Posts
    22
    it is air cooled but it has a flooded evap (water in tubes). mcquay int. plugged them because of glycol leaking into refrigerant system

  6. #6
    Join Date
    Dec 2011
    Posts
    108
    The two drains on bottom are in and out. The evap is split verticlely.Min water in feet is 6.1min.14.2nom.35.2max.Was circuit in pressure control or subcool mode?

  7. #7
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,596
    If this is the machine I'm thinking of I think it does have a flooded evaporator.

    With that being said, it's far easier to check the water side IMO and start there. Get the book and look up your design gpm, ft head drop, and figure your psi drop across the barrel and see what you have going on there first. Install a port where you can check pressure drop with the same gauge and go from there.

    SN: The machines we had are no longer with us due to a ruptured tube which conveniently filled the liquid line with glycol.

  8. #8
    Join Date
    Jun 2012
    Location
    West Virginia
    Posts
    22
    that will help if I can put a gauge on the drains just to check for now. I do have the IOM with flow chart. I THINK this machine controls in subcool mode at start up and as soon as it starts to load up it goes into low evap warning and will not allow the compressor to load due to that fact... I will have some time tom. to really check things out. I am going to start with water flow

  9. #9
    Join Date
    Feb 2003
    Location
    Wichita Ks
    Posts
    1,507
    they should be a port on the inlet and outlet close to the barrell, it may be under the insulation. dont forget to calculate for glycol on flow. has anyone pull the strainer and check? This is a flooded evap. also make sure of the glycol mix and the controller needs to be set cool with glycol. Then it can be adjusted to where you need it.

  10. #10
    Join Date
    Jun 2012
    Location
    West Virginia
    Posts
    22
    ok. I checked the pressure at the two drain fittings with the same gauge and found 8 PSI drop (water temp is 75 deg F). I just used 8 psi X 2.31 to convert to ft of water 18.48. There is a presure drop factor table in IOM 1.664 at 40% propylene glycol. do I multiply 18.48 by 1.664? wow that doesnt look right. 30.75... start up sheet was 48 deg ewt and 44 lwt 11.5ft pd and this was without glycol. There is no strainer in system. there should be a screen in suction diffuser but there isnt any more than 2psi drop across it. controller is set to cool with glycol

  11. #11
    Join Date
    Jan 2011
    Posts
    1,223
    It sounds to me like your flow is correct. If it was 11.5' at start-up with water then you would multiply that times the 1.664 and you'd come up with 19.1' which is close to what you have.

  12. #12
    Join Date
    Jun 2012
    Location
    West Virginia
    Posts
    22
    both ckts are low evap ref pressure. After I determined flow today I started checking ckt one. From what I read in the operation manual upon start up h exv performs a pre-open function and opens to 3000 steps. when I look in the exv sight glass I hear the valve driving but no movement is observed. I wanted to put the valve into test mode and confirm but I would have to have the manager password and I havent been able to find it. operator is 0100. When running in evap press low comp. goes 0% slide and exv says 3000 which is max steps for 0% slide. I dont think valve is moving. 0 slide, max exv, no press drop across driers, 75 ewt and no delta T

  13. #13
    Join Date
    Jun 2012
    Location
    West Virginia
    Posts
    22
    circuit 2 is locking out on the same thing and that made me want to check the water flow. ckts have seperate circuit controllers so I am going to start with ckt 1 first. I have never seen the exv move in the sight glass but shouldn't it be pretty noticeable?

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