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  1. #1
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    Jun 2006
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    High Superheat, Losing Temp

    In a large drive-in -10 freezer with dual evaps, the west evap only has frost on the top third of the coil after 5 hours (the east evap is frosted evenly) and the superheat is high, around 30 degrees measured just outside the box. It's definitely being underfed. I can't get up to the evap to study it without them removing tons of product, but if the TXV bulb has ice buildup around it could that cause it to underfeed? I would think that might only cause it to react slowly. The only other thing I can think of is the TXV sensing bulb has lost part of its charge.

    It seems to feed really well when it first comes out of defrost, judging by watching the suction pressure. The box comes down to around 5 degrees in 30-60 minutes or so, and then the liquid feed just seems to taper off. As the freezer starts warming up to around 12-13 degrees, the superheat continues to climb and compressors keep unloading because the suction pressure drops off slowly. It almost seems like moisture freezes in the TXV but I don't think that's the case because how would it ever thaw out with electric defrost? The east evap works like a charm.

    I wish I could get more info but they have food stacked up to the evap and because it's staying frozen they don't want me to mess with it. I guess they'd rather wait until it's an emergency.

  2. #2
    Join Date
    Sep 2002
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    12,715

    It's only one evap and always the same one

    I would suspect a bad power element on that TXV first I think - losing it's charge. With a warm coil it opens the valve more but then then as the suction line cools the underfeeding is more noticable.

    I would think that melted ice would travel in the system and then not always return to the same evap, but why not just change the drier anyway? That little down time won't hurt them.

    And why not work it out with the shipping manager to be there when the product blocking access to the evap is taken out?

    Another thought is that in that same circumstance I have laid plywood across the top of the product in order to get across to work on the evaps.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  3. #3
    Join Date
    Jun 2006
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    Omaha, Nebraska
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    861
    ^ I agree. Sounds like a good assessment.

    Getting them to stock a certain way is like pulling teeth but I will leave that to the manager.

    Thanks!

  4. #4
    Join Date
    Sep 2002
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    12,715

    How is it living in St. Croix ?

    Have you always lived there? Or if not; how long have you been living there?

    I like Tortola quite a lot but I don't know what it would be like living there.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #5
    Join Date
    Jun 2006
    Location
    Omaha, Nebraska
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    Quote Originally Posted by Poodle Head Mikey View Post
    Have you always lived there? Or if not; how long have you been living there?

    I like Tortola quite a lot but I don't know what it would be like living there.
    I've only lived here a few months, but have been visiting for years. The climate is similar to Tortola from what I've heard but the culture is like no other. Many of the local people are unskilled and don't like to work or learn much. They are not used to business and schedules and just don't understand such things. It can be frustrating to people from the states, (I'm from Nebraska) but for someone like me it's an advantage. I can make a fortune doing HVACR because just getting someone to show up is a challenge in most cases.

    Example- last week a small market had their freezer go down. They called a local guy. He shows up, finds the breaker tripped, resets it and leaves. A while later it trips again. He never bothered to check anything to see why it tripped. Things like that happen all the time here. Finding parts is also impossible. I have to buy everything and have it shipped down. Even fuses and fan belts are unavailable.

    I enjoy it, though. It's a welcome change of pace.

  6. #6
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    Sep 2005
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    florida
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    5,514
    Quote Originally Posted by Poodle Head Mikey View Post
    I would suspect a bad power element on that TXV first I think - losing it's charge. With a warm coil it opens the valve more but then then as the suction line cools the underfeeding is more noticable.

    I would think that melted ice would travel in the system and then not always return to the same evap, but why not just change the drier anyway? That little down time won't hurt them.

    And why not work it out with the shipping manager to be there when the product blocking access to the evap is taken out?

    Another thought is that in that same circumstance I have laid plywood across the top of the product in order to get across to work on the evaps.
    I agree sound's like a weak power head. But as for the I have laid plywood across the top of the product in order to get across to work on the evaps.[/QUOTE] That's alot nicer than what I do if they wont move the
    product I'll just stand on it and work. Than after that I never have any trouble getting product moved out of my way.
    I love the smell of phosgene first thing in the morning:

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  7. #7
    Join Date
    Mar 2008
    Location
    Banana Republic,Florida
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    400
    Quote Originally Posted by man from trane View Post
    In a large drive-in -10 freezer with dual evaps, the west evap only has frost on the top third of the coil after 5 hours (the east evap is frosted evenly) and the superheat is high, around 30 degrees measured just outside the box. It's definitely being underfed. I can't get up to the evap to study it without them removing tons of product, but if the TXV bulb has ice buildup around it could that cause it to underfeed? I would think that might only cause it to react slowly. The only other thing I can think of is the TXV sensing bulb has lost part of its charge.

    It seems to feed really well when it first comes out of defrost, judging by watching the suction pressure. The box comes down to around 5 degrees in 30-60 minutes or so, and then the liquid feed just seems to taper off. As the freezer starts warming up to around 12-13 degrees, the superheat continues to climb and compressors keep unloading because the suction pressure drops off slowly. It almost seems like moisture freezes in the TXV but I don't think that's the case because how would it ever thaw out with electric defrost? The east evap works like a charm.

    I wish I could get more info but they have food stacked up to the evap and because it's staying frozen they don't want me to mess with it. I guess they'd rather wait until it's an emergency.
    is this the same box that keeps acting up i think we talked about this what 2-3 weeks about it?this is a box from hell?hey is the powerhead a SZP OR VZP THAT would be a pressure limited power head is the suction psi going above the suction set point at any time?sometimes you feed sometimes you dont depending on the psi.it happen to me once with a wall reach/in 80ft.

  8. #8
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    Jun 2006
    Location
    Omaha, Nebraska
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    861
    Quote Originally Posted by gatorfan9606 View Post
    is this the same box that keeps acting up i think we talked about this what 2-3 weeks about it?this is a box from hell?hey is the powerhead a SZP OR VZP THAT would be a pressure limited power head is the suction psi going above the suction set point at any time?sometimes you feed sometimes you dont depending on the psi.it happen to me once with a wall reach/in 80ft.
    Same box, different evap. I haven't paid much attention to this evap until last weekend I was at the store shopping and saw the west coil with frost only on the top few rows of the coil shortly before defrost was scheduled, and the box temp was 10 degrees. (This store is my primary account so fortunately I have lots of time to play with it and learn. ) I don't know what a "pressure limited power head" is.

    The suction pressure starts out around 23 psi (404A) after defrost and slowly comes down to the target of 13.1 (-25F) within an hour or less. Both evaps start defrost at the same time, the west evap usually terminates 3-4 minutes later than the east. The west side of the freezer is usually 3-4 degrees warmer than the east also. Once at target the Com-Trol does a good job of keeping it between 11.5 and 15 psi.

    One thing that has changed. I found the pressure sensor reading 7 psi high so I re-calibrated it. So now the system is running at a higher pressure than it used to. It used to run around 10 psi and never meet the target (the target would have been 6 psi with the sensor reading high), now it's 13.1.

    The plate on the front says the low temp side was designed for -28 degrees suction, also a decal on the low-temp accumulator says the same thing. BUT the documentation from Com-Trol says -25 degrees and that was where it was set when I got there. Could Com-Trol have entered the wrong number, or does this just mean -28 is what the machine is capable of but it doesn't need to be that low? Why the discrepancy? It's the same on the medium temp side. Source says 13 degrees, Com-Trol docs say 15.

  9. #9
    Join Date
    Mar 2008
    Location
    Banana Republic,Florida
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    400
    Quote Originally Posted by man from trane View Post
    Same box, different evap. I haven't paid much attention to this evap until last weekend I was at the store shopping and saw the west coil with frost only on the top few rows of the coil shortly before defrost was scheduled, and the box temp was 10 degrees. (This store is my primary account so fortunately I have lots of time to play with it and learn. ) I don't know what a "pressure limited power head" is.

    The suction pressure starts out around 23 psi (404A) after defrost and slowly comes down to the target of 13.1 (-25F) within an hour or less. Both evaps start defrost at the same time, the west evap usually terminates 3-4 minutes later than the east. The west side of the freezer is usually 3-4 degrees warmer than the east also. Once at target the Com-Trol does a good job of keeping it between 11.5 and 15 psi.

    One thing that has changed. I found the pressure sensor reading 7 psi high so I re-calibrated it. So now the system is running at a higher pressure than it used to. It used to run around 10 psi and never meet the target (the target would have been 6 psi with the sensor reading high), now it's 13.1.

    The plate on the front says the low temp side was designed for -28 degrees suction, also a decal on the low-temp accumulator says the same thing. BUT the documentation from Com-Trol says -25 degrees and that was where it was set when I got there. Could Com-Trol have entered the wrong number, or does this just mean -28 is what the machine is capable of but it doesn't need to be that low? Why the discrepancy? It's the same on the medium temp side. Source says 13 degrees, Com-Trol docs say 15.
    were you able to look at the power head sticker on the tev?if its not feeding right i would spend some time on that valve maybe take it apart look at the guts, at the power head make sure the piston is moving freely?

  10. #10
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    Sep 2005
    Location
    florida
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    Is this box tied to a rack system?
    I love the smell of phosgene first thing in the morning:

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  11. #11
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    Jun 2006
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    Omaha, Nebraska
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    Quote Originally Posted by crackertech View Post
    Is this box tied to a rack system?
    Yes, a Source low/med temp rack.

  12. #12
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    Sep 2005
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    Quote Originally Posted by man from trane View Post
    Yes, a Source low/med temp rack.
    Ok than next step check power head type should be a sz not a szp which is a
    pressure limited power head they tend to not work well on rack systems.
    I love the smell of phosgene first thing in the morning:

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  13. #13
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    Jun 2006
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    Quote Originally Posted by crackertech View Post
    Ok than next step check power head type should be a sz not a szp which is a
    pressure limited power head they tend to not work well on rack systems.
    Thanks!

    Ok, can someone please humor me and explain what a pressure limited power head does? I'm not familiar with the term. I thought they just controlled superheat by comparing the evap outlet temp to the suction pressure and throttling accordingly. I guess the pressure limiting one does something extra?

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