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  1. #27
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    Dec 2007
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    Well youre half right. Power is broken to the LLS, fans and T-stat. This allows the compressor to pump down.. This allows the compressor to pump down.. This allows the compressor pump down. When a T-stat opens the compressor pumps down, when the LLS loses power the compressor pumps down Ref 101 close the refrigeration supply to the compressor and the pressure drops till the LPS opens. IT PUMPS DOWN..

    Geezzz "professionals"

  2. #28
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    Mar 2008
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    Quote Originally Posted by mdnbiker View Post
    Well youre half right. Power is broken to the LLS, fans and T-stat. This allows the compressor to pump down.. This allows the compressor to pump down.. This allows the compressor pump down. When a T-stat opens the compressor pumps down, when the LLS loses power the compressor pumps down Ref 101 close the refrigeration supply to the compressor and the pressure drops till the LPS opens. IT PUMPS DOWN..

    Geezzz "professionals"
    Bugger! you got me.
    I will find a reference to back up my assertion, but not tonight. I've been doing it this way since a lovelocks (now owned by heatcraft) engineer told me to do it that way in the late 80s.
    All our supermarket systems here shut down the liquid line and energise a suction modulating valve to restrict the suction line on low temp cases and rooms when they go on defrost. They don't pump down first.
    more to come.
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  3. #29
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    Feb 2005
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    Quote Originally Posted by Slatts View Post
    Bugger! you got me.
    I will find a reference to back up my assertion, but not tonight. I've been doing it this way since a lovelocks (now owned by heatcraft) engineer told me to do it that way in the late 80s.
    All our supermarket systems here shut down the liquid line and energise a suction modulating valve to restrict the suction line on low temp cases and rooms when they go on defrost. They don't pump down first.
    more to come.
    I have been reading along, this is the first mention of a "suction modulating valve". I was trying to figure how an evap full of refrig in defrost wouldn't just keep raising the suction pressure and bring on the compressor untill you had an empty evap coil and a pumped down system western hemisphere style.

  4. #30
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    Mar 2008
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    North Queensland, Australia
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    See page 9
    [IMG]file:///C:/WINDOWS/TEMP/moz-screenshot.jpg[/IMG]
    Attached Images Attached Images   
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  5. #31
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    North Queensland, Australia
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    Quote Originally Posted by phosgene View Post
    I have been reading along, this is the first mention of a "suction modulating valve". I was trying to figure how an evap full of refrig in defrost wouldn't just keep raising the suction pressure and bring on the compressor untill you had an empty evap coil and a pumped down system western hemisphere style.
    Check the wiring diagram I attached to post number 21 (page 2)
    The modulating valves are only used on parallel racks. they de-energise on defrost. I've had them burn out their coils occasionally. The cases, needless to say go on high temp alarm.
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  6. #32
    Join Date
    Jul 2007
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    N.C.
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    712
    Don't assume a pump down. I've worked on both. If it is a PDS you need to find it. Check tstat or Temp control.

  7. #33
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    Feb 2007
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    Northern NJ
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    646
    Quote Originally Posted by phosgene View Post
    I have been reading along, this is the first mention of a "suction modulating valve". I was trying to figure how an evap full of refrig in defrost wouldn't just keep raising the suction pressure and bring on the compressor untill you had an empty evap coil and a pumped down system western hemisphere style.
    i believe slatts was refering to a sorit when he mentioned suction modulating valve. as for the compressor coming on in defrost as the pressure rises, it cannot, because the compressor is wired directly off of clock terminal 4, parallel with the solenoid valve, making it a drop system. my co does this in certain situations, when liquid in the coil will help evenly distribute the heat of the electric heaters. it results in a faster defrost, we use it in boxes where equipment is not properly sized and we need refrigeration all the time without off cycles between defrosts.

  8. #34
    Join Date
    Jan 2007
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    Kansas the real Oz
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    17

    Pump down

    Use to be responsible for a Hussmann Chino rack, electric defrost. All low temp circuits had a suction line solenoid & LLSV to strand the refrig. during defrost, no pump down. Speeded up defrost markedly.
    Mike

  9. #35
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    Mar 2008
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    Quote Originally Posted by tjc76 View Post
    i believe slatts was refering to a sorit when he mentioned suction modulating valve. as for the compressor coming on in defrost as the pressure rises, it cannot, because the compressor is wired directly off of clock terminal 4, parallel with the solenoid valve, making it a drop system. my co does this in certain situations, when liquid in the coil will help evenly distribute the heat of the electric heaters. it results in a faster defrost, we use it in boxes where equipment is not properly sized and we need refrigeration all the time without off cycles between defrosts.
    Quote Originally Posted by yamoon View Post
    Use to be responsible for a Hussmann Chino rack, electric defrost. All low temp circuits had a suction line solenoid & LLSV to strand the refrig. during defrost, no pump down. Speeded up defrost markedly.
    Mike
    At last! believers!
    I was talking to a local heatcraft ginger beer at a party on Friday night. He says the reason the compressor shouldn't pump down before shutting down on defrost is to help distribute the heat through the coil by having a higher density medium to conduct the heat throughout the evap, allowing lower wattage heaters and faster defrosts.
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  10. #36
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    Feb 2005
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    small island in the Pacific Ocean
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    Interesting. I have never seen this set up. May be time for an experiment. Thanks for the info. Faster defrosts are a good thing.

  11. #37
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    Dec 2007
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    I never said I didn't believe you. I'm sure you were correct for the equipment you were refering to but, this thread was for a Heatcraft evap, and the installation guide for this type of evap calls for a pump down defrost. I just don't see that type around here and apologize if I gave the impression you were wrong across the board about any and all systems. It was good and educational to work this out for both sides. If Heatcrafr people agree that the gas should stay in the evap then they should change the manual, since warranty does not cover improper installation.

  12. #38
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    Feb 2007
    Location
    Northern NJ
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    646
    Quote Originally Posted by mdnbiker View Post
    I never said I didn't believe you. I'm sure you were correct for the equipment you were refering to but, this thread was for a Heatcraft evap, and the installation guide for this type of evap calls for a pump down defrost. I just don't see that type around here and apologize if I gave the impression you were wrong across the board about any and all systems. It was good and educational to work this out for both sides. If Heatcrafr people agree that the gas should stay in the evap then they should change the manual, since warranty does not cover improper installation.
    we have several heatcraft evaps we have done this on, chandler, bohn, climate control. i would not do it in every instance, it is situational, and if your equipment is still under warranty, i would advise contacting heatcraft before making changes.

  13. #39
    Join Date
    Jan 2007
    Location
    Kansas the real Oz
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    17

    Pump down

    We seem to be hijacking this thread, but in addition to the Chino rack I spoke of earlier, I've used this method after a remodel to strand refrig. during off cycle on MT circuits on an old Protocol because the receiver was too small to hold all of the refrig. pumped out of the long pipe runs. I used a sorit that did not require a connection to the high side. I believe it is called a psorit.
    Mike

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