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Thread: Beginning to test.

  1. #1
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    Beginning to test.

    I've started testing. At least in a preliminary fashion.

    Regards, Stew.....

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    Newbie alert.... The discharge and liquid lines are very hot. This seems to signify a problem, but I'm not sure what that problem is. The system is pulling down fine, but I know the compressor shouldn't be getting that hot. The stable running pressure on the suction line is 60PSI, which is a bit north of what I expected. Do I need to make adjustments to the TXV???
    Regards, Stew.....

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  3. #3
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    How hot? Those can run upto 110C.
    And sounds like the pump is simply cavitating on some air.


    If you have a cooling question or concern feel free to contact me.

  4. #4
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    i don't want to sound like a but could you please hold your camera horizontally next time

    I like large posteriors and I cannot prevaricate

  5. #5
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    i don't want to sound like a but could you please hold your camera horizontally next time
    It stands to reason that I realized that and will undoubtedly make amends with the next video... hehe
    Regards, Stew.....

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  6. #6
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    Quote Originally Posted by n00b 0f l337 View Post
    How hot? Those can run upto 110C.
    And sounds like the pump is simply cavitating on some air.
    The pump may be cavitating, and surely the next time I fill the system I'll see if I can do something about it... However, usually these things work themselves out. The system was running for considerable time. There were no changes. In fact it got worse.

    The system stabilized some, but I couldn't get the system to even frost on the suction line. It stabilized at 40PSI at the suction line give or take. The TXV outlet went as low as 24F but no lower. The return gas was ~10 degrees warmer. Its pretty clear that I'm getting good heat transfer. The system pulled from 74 to 50 degrees in about 10 minutes. So pump flow isn't an issue. The condenser pump did well. No leaks there and the condenser water was balmy at the least. Didn't even peak 80 degrees.

    Condenser pressure was 190-205 PSI at the most, and suction pressure was ~38-44 PSI at the most. The Sight Glass was not completely full, however as I have added charge the suction pressure rises and stays that way. I'm reluctant to add charge further until I have a good sense of what I'm doing.

    The coldest I got the water was 30F. It then hovered between 30 - 31 F. So I'm on the right track.

    I will say, the discharge line temp came down after I added charge. Clearly there wasn't enough refrigerant coming back. Anyways, help is appreciated.

    P.S. I was having a ball out there today.... hehe
    Regards, Stew.....

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  7. #7
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    Any help?

    I have a distinct feeling that I'm undercharged. Superheat is considerable given the pressure at the suction line being at 40PSI and the temp above freezing. However, every time I add charge the suction pressure rises and it does not go down...

    Do I need to significantly change the setting on the TXV regarding the superheat? I have a feeling its doing some excessive hunting. Again, might just be my experience level with charging...
    Last edited by Stewie007; 11-04-2013 at 07:52 AM.
    Regards, Stew.....

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  8. #8
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    I think I may have a solution for my pump cavitation problem. I've done some additional research and I agree that it appears to be a cavitation issue. I'm likely going to have to redesign the pump discharge to be a vertical system with a bleed valve. Currently it is a horizontal discharge and that may be causing the pump some difficulty in removing air bubbles. I'm still curious as to why the first fill didn't produce this problem.

    I wonder if the glycol (being somewhat viscous) caused a vapor barrier behind the impeller that caused an internal air bubble that couldn't force its way out. Sort of the way soapy water forms a bubble. Once I filled, at static pressure it could have been enough to maintain itself in that tiny space. Once running the bubble couldn't be ejected. It might have settled at the top of the volute and stayed... Which is odd... Of course, that is all just a supposition... Either way, it seems to be cavitation.
    Regards, Stew.....

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  9. #9
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    You can also prime the pump manually with.... another pump. Basically buy a small pump and use it to pump fluid into the main pump before filling the system.


    If you have a cooling question or concern feel free to contact me.

  10. #10
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    I could, but that's difficult given the setup... Maybe Fill it backwards???
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  11. #11
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    I feel kind of dumb... I forgot to insulate the TXV Bulb. I should probably do that before making any assumptions about charge... I will examine the location of the bulb as well just to make sure its in a good position and nice and snug.

    Edit: I did also have a nice long conversation with some folks around here. One of the HVAC Techs gave me some good pointers. Helped me understand the TXV operation a little better. Aside from insulating the bulb, I'll make the adjustments this Saturday.

    Then its round 2!
    Last edited by Stewie007; 11-06-2013 at 11:36 AM.
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  12. #12
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    Today is the big day! >=)

    Here's to hoping I get this thing down to 0F!
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  13. #13
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    Bad news. My impeller is busted.

    I found out what was going on. The pump wasn't cavitating at all. In fact, it was pumping very well and self priming as designed. The pump suction was nothing short of impressive. Unfortunately, that means I can't refill my system without expending a ridiculous amount of effort when I have to drain it again. The bushing somehow broke off of the impeller and thus I need a new one.
    Regards, Stew.....

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  14. #14
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    Well I did fill the thing back up. I'm going to buy a new impeller. The bushing is missing (obviously broken off). So the impeller slides forward. It doesn't make that noise when I run it dry. It only happens when its got fluid; and glycol isn't enough to give the pump motor any problem (it made it with water last time I ran it too). In the meantime I'm testing. I've almost got the right charge inside. The TXV is better behaving now that I've added some charge. Its pulling down very quickly... In fact while I was adding charge it cut off and pumped down.

    Not quite there with the charge yet, but getting close.
    Regards, Stew.....

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  15. #15
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    It appears that i have somewhere between 3.5 - 4.5 lbs of charge. <--- It could be less, but I just didn't take a beginning cylinder weight. The URI website says the shipping weight is 32 pounds, but I don't know that I can trust that.

    I'm done for the week, but some very promising results. The return gas got itself down to 11 degrees at the lowest. I didn't get any shots because I was busy baby sitting a few things. Unfortunately, with both pumps running and a the other odds and ends I was blowing the garage circuit a few times. The compressor is likely drawing around 10 amps. So that leaves 5 for the two pumps, solenoids, and fans.

    After consideration, I believe the activation of the two solenoids connected to the power relay are causing the trip. It happens about 10 minutes after starting (coincidentally the time setting for the delay). I've got to find a way to plug into a separate circuit, or I'll never be able to test the bloody thing through a full cycle.

    I relocated the TXV bulb to the evaporator outlet, and my sight glass is now clear. My biggest concern is with how much refrigerant is in the system. My receiver has a 3lb holding charge capacity. The system probably contains slightly more than that, but of course it isn't all in the receiver.

    Bottom line, next week will mean the final adjustments.

    Superheat = ~17F (Might have to do with my tweaking the TXV last week, will make minor adjustments)
    Sub Cooling = ~10F (Right on target.)

    Suction Pressure - 35-37PSI
    Discahrge Pressure - 310PSI (This is likely high due to the incorrectly adjusted TXV, or I may have to remove some charge. I'm betting on the former.)

    Lowest Fluid Temp so far = 30F (Dang circuit breaker. Who places a 15 amp circuit in a garage? Seriously. 20 Amp please?)

    I will have to get a new impeller, but in the meantime all is good.
    Last edited by Stewie007; 11-10-2013 at 10:40 AM.
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  16. #16
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    So what do y'all experienced folk think? Should I worry about that high discharge pressure? Or is that just due to the heat of compression due to higher superheat? (Which I can adjust).

    I gotta say, this worked out perfectly. It actually works as designed. No real tuning nightmare, just pure unadulterated bliss. I never felt so excited in my life! Well, at least as far as accomplishments go... :p
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  17. #17
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    New Impeller is in hand. Lets see if we can't get down to temp this weekend!

    Friday : Replace Impeller and run system checks and build heat exchange coil (minor job).
    Saturday : Take system to minimum design temperature!

    I'm excited. No more setbacks this time. Just run it! >=)
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  18. #18
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    I like your plans, then on Sun. you can chill a cpu.

  19. #19
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    Well, I could.... but the next phase is actually building the enclosure, then getting the parts. So that's a bit off... :p

    One thing at a time
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  20. #20
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    Impeller changed. Bushing busted. New seal as well.

    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  21. #21
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    In continuing my investigation, I have made an additional discovery. Upon taking apart the pump once more when I changed the impeller I neglected to remove the rubber seal that was in there. Somehow my idiot brain thought that it was part of the pump. However, this orange seal was in place.

    This is not a design seal. This seal is too thick, and as a result, the gap between the thrust washer and the front of the pump meant that the impeller would always rock as it spun. Evidently, the micro vibrations that resulted probably caused the breakage of the impeller bushing. Although this seal created a single millimeter gap between the volute sealing surface and the pump housing, it is enough to cause the impeller to shudder.

    It is my conclusion that the guy I got it had to replace parts just as I have had to do. That is probably what lead him to sell it. It wasn't that old when I bought it. I got quite a steal. I am willing to bet that he started having problems when he switched to the new seal.

    Tomorrow I will be able to FINALLY run the dang thing without all that noise. ^_^

    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

  22. #22
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    Regards, Stew.....

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  23. #23
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    Looks good Stew !
    Glad you got that pump problem sorted out

  24. #24
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    Regards, Stew.....

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  25. #25
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    Will post temps after dessert. Its taking a while to pull down, but that was because of some issues that I had. A bit of adjustment and it looks good.

    The only problem is the pressure at start-up. Its meant for low temp applications, so when it is working with...say... 63 degree coolant, then the high side pressure spikes quite a lot. It gets as high as 375PSI. That said, pressure normalizes over time and we're at 250PSI and ~25PSI. That changes as the coolant gets colder. Pretty normal, but man its taking a while.

    What is normal pull down time for most? I'm on 2 hours from 65F. Its down to ~15F now. 25 degrees per hour. Not bad? I just don't have a comparison to benchmark against, hehehe.
    Regards, Stew.....

    - This message brought to you by Frank Lee E. Snutz

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