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  1. #1
    Join Date
    Feb 2006
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    Perlick glycol chiller?

    Did a compressor change-out on one of these today. At start up found high side a little below normal and suction at 12 psi. I was thinking. "Is this thing restricted". So i'm looking around for a cap tube. No cap-tube. Okay, "where's the TXV"? No txv! But, i did find an Constant pressures expansion valve. My pressure were 130 hi and 12 low after weighing in charge. Bath temp was 66F. What do you all think? It is cooling. But, i don't know what kind of pressures to expect on this system. Also didn't really like the high SH.
    Thanks

    Perlick M# 4404

  2. #2
    Join Date
    Jun 2003
    Location
    Chicago, IL
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    4,426
    I've never worked on a glycol chiller, but......

    a AXV will have high superheat on a hot pulldown.

    130 seems like really low head, especially on pull down.

    12 PSI seems like low suction, but you didn't say what refrigerant its running.

    If your sure the charge is right, I would suspect a restriction or that someone fiddled with the AXV settings to try an fix a problem that was really a failing compressor.

  3. #3
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    Feb 2006
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    Phoenix,AZ
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    Oh yeah,
    It's running 134a. I don't think anybody's messed with the valve. As it still looked to be pretty well insulated. On a AXV. Isn't the purpose of it. To maintain constant evap PSI.
    So regardless if the bath is 66F or 28F. Pressure will still be the same? I'm trying to figure out if i have a problem with this cooler or not. The original compressor locked up. Which i beleive was caused by a refrigerant leak that i also repaired today. 12 psi wouldn't be low suction if the bath was at temp.

  4. #4
    Join Date
    Jan 2010
    Location
    Arizona
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    106
    scratch that, looking at wrong unit.

  5. #5
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    Aug 2002
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    Southold.calm
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    5,678
    Disconnect the circulating pump and pull the bath temperature down. Weighing in the charge puts you in the ball park but you may have to adjust it slightly up or down, in your case add a few oz more.

  6. #6
    Join Date
    Aug 2006
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    Wisconsin
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    Did you change the FD? Is there an inlet screen on the AXV. No nitrogen during brazing will plug up those screens.
    Buy American! The job you save may be your own.

  7. #7
    Join Date
    Jun 2003
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    Chicago, IL
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    Quote Originally Posted by kbghdg View Post
    On a AXV. Isn't the purpose of it. To maintain constant evap PSI.
    that is correct, and its also one of the major drawbacks of an AXV. during times of high load, evaporator pressure naturally increases due to faster evaporation rates. An AXV detects this and REDUCES refrigerant flow, when ideally flow should increase. The reduced flow, combined with fast evaporation results in high superheat.

  8. #8
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    Feb 2006
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    Phoenix,AZ
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    Quote Originally Posted by hvac_superman View Post
    Did you change the FD? Is there an inlet screen on the AXV. No nitrogen during brazing will plug up those screens.
    Yes i replaced the copper spun dryer with a 032s. And i used nitro. I haven't messed with the AXV at all. I didn't know if i needed too or not. This is my first AXV i ran across.

  9. #9
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    Quote Originally Posted by pecmsg View Post
    Disconnect the circulating pump and pull the bath temperature down. Weighing in the charge puts you in the ball park but you may have to adjust it slightly up or down, in your case add a few oz more.
    I had the pump off when i first started it up. After a couple minutes. Thinking i have a problem. I turned the pump on. My suction then spiked up to around 28 psi. And i was i like. "it's not restricted now".. But, then a couple seconds later suction dropped back to 12 psi.

  10. #10
    Join Date
    Dec 2008
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    Dixiana, AL
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    Quote Originally Posted by kbghdg View Post
    12 psi wouldn't be low suction if the bath was at temp.
    You answered your own question in that statement, because you already knew that an axv is nothing more than a pressure regulator. What is your design bath temp? As far as condenser pressure, if it's water-cooled on R134A, 130 psig might be a touch high. If it's air-cooled, what's your ambient?

  11. #11
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    Quote Originally Posted by klove View Post
    You answered your own question in that statement, because you already knew that an axv is nothing more than a pressure regulator. What is your design bath temp? As far as condenser pressure, if it's water-cooled on R134A, 130 psig might be a touch high. If it's air-cooled, what's your ambient?
    Ambient probally around 80 up in the dark ceiling on top of the walk-in.(Why do these idiots put them up there? ) The machines running fine. If the frosted glycol lines in the walk-in are an indication. Because thats all i saw today as i was working on something else. But, if my axv is actually restricting flow. Head would drop also. Correct?

  12. #12
    Join Date
    Dec 2008
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    Dixiana, AL
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    Quote Originally Posted by kbghdg View Post
    Ambient probally around 80 up in the dark ceiling on top of the walk-in.(Why do these idiots put them up there? ) The machines running fine. If the frosted glycol lines in the walk-in are an indication. Because thats all i saw today as i was working on something else. But, if my axv is actually restricting flow. Head would drop also. Correct?
    Correct. There is a point of restriction if it's caught early enough (when there's little enough restriction) that head will increase minutely, but it's hardly worth mentioning. For all practical purposes, when you starve the evap due to restriction, your condenser becomes a lot larger than it needs to be for the amount of refrigerant going into it (because your comp is pumping less) at any given conditions, thus causing a drop in head pressure. On 134 you're at about 102* saturated condensing temp, and according to this quote, you're not positive about the ambient at the condenser - could be lower, which would put your head closer to being right where you might want it. Things just don't sound that bad from where I'm sitting. The $64,000.00 question is, "Is it working correctly during pulldown and at setpoint?"

    I believe you need to provide yourself with a little more info to be convinced it's working, based on everything you know to be a fact: What is the ambient at the condenser ("around 80*" is a large number)? What do you think your head should be based on the ambient at the condenser? What is your subcooling? Did pulldown require an inordinate amount of time? What is your setpoint and are you holding with no issues despite fluctuation in load?

  13. #13
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    Set point is 28F. I know just by looking at the glycol lines it's running below 32F. I decided it wasn't worth the effort to take a look at it today. As i'm almost certain it's running the way Perlick designed it. A txv may have been a better choice. But, i'm sure it would of cost them $5.00 more so they went with a AXV instead.

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