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  1. #1
    Join Date
    Dec 2007
    Posts
    49

    Hmm problem adding (wiring) a pumpdown cycle

    This customer of mine has lost two compressors in the last seven years.
    (Med. temp remote unit 1 HP 208/230, 1ph, R12 coverted to Hot Shot.) Happens in winter. I'm suspecting flooded starts due to liquid migration back to compressor. Yes CC Heater is good. Told him I would install a LLS with a pumpdown cycle to help prevent the problem again. Thought I could simply wire the LLS (Sporlan dual voltage MKC-1) in series after the thermostat. However the contactor never pulled in despite LLS powered open and 40 psi low side. Tstat has 240 volts at terminals when 'open' and Yes I wired the LLS for the 240 volt version. This unit was assembled by another company long before I got there so I dont have a traditional schematic to follow. My electrical knowledge is being tested here. (Admittedly not my strongest suit) Here's the weird part... the contactor will pull in when I manually push it in and will remain pulled in until, the tstat opens again. I can't figure out how to wire the LLS. Cant see why I cant just wire in series after the Tsta. Any clues...?

  2. #2
    You didn't mention what the LPC is set for?

  3. #3
    Join Date
    Feb 2006
    Location
    Phoenix,AZ
    Posts
    2,760
    You did install a low pressure control to energize your contactor? Right

  4. #4
    Join Date
    Dec 2007
    Location
    tennessee
    Posts
    25
    Yes, what is lpc set for and sounds like you may have bad contactor. With tstat closed check voltage at contactor coil. Coil may be week. GL

  5. #5
    Join Date
    Sep 2005
    Location
    florida
    Posts
    5,495
    The first thing I would do is lose the hot sh!@.Then work on the lls.
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  6. #6
    Join Date
    Dec 2007
    Posts
    49
    LPC is properly set. Prob is power isn't even making it to the LPC because the contactor isn't being pulling in. For an experiment I wired TStat back to original and all works well. (I have LLS powered temporarily through another source). It's not the LPC.

    I'm wondering if one side of contactor coil is constantly powered w one leg on 110 and other side goes through Tstat. And once I introduce the LLS into the circuit it creates a shunt circuit where not enough voltage can pull the coil in. Electrical sharpies does this make sense...?

  7. #7
    Are you saying you have the LLSV and the contactor coil in series? That is wrong. The tsat needs to control the LLSV only, and the contactor coil energized through the LPC. You still did not mention LPC values.

  8. #8
    Join Date
    Feb 2009
    Location
    Wisconsin
    Posts
    304
    It wont pull in the contactor as you have it wired. Before you started, control power went from one line ,through the tstat then back to the contactor coil,correct? Then you tapped that line after the tstat and wired it to the solenoid. You dont have 240 volts to the solenoid. The easiest way to fix it is to use the power from the evaporator to power the solenoid. Tap off evap. power,take one line through tstat then to one line of solenoid. Take second line from evap. to second line of solenoid. Then make sure your low press. switch is set correctly.

  9. #9
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    i posted in the other thread that was started

    seems like a voltage drop somehwere is causing the issue. not enough power to pull in the contactor, but enough to hold it when you give it that push.

    t-stat should control only the LLS and low pressure control should control the contactor outside
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  10. #10
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,543
    Quote Originally Posted by smilies View Post
    Are you saying you have the LLSV and the contactor coil in series? That is wrong. The tsat needs to control the LLSV only, and the contactor coil energized through the LPC. You still did not mention LPC values.
    Line 1 to one side of the t-stat then other side of t-stat solonoid coil other side of coil to line 2.

    Compressor contactor one side of the coil to line 1, other side of coil to LP controll and other contact on LP control to line 2.

    Defrost timer breaks l.l. solonoid coil.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  11. #11
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,947
    OH!!!

    Yeah. Loads in series are a VERY bad idea on an AC circuit.

    There are 2 circuits required on the control.

    You need to have one for the LLSV and one through the safeties that runs the compressor.

  12. #12
    Join Date
    Sep 2006
    Location
    Chicago
    Posts
    474
    Did you add a new contactor? I had this happen to me on a siemens contactor brand new out of the box. Old contactor went out replaced with a new siemens and it wouldnt pull in for whatever reason unless i nuged it just a hair. Checked voltage and everything. Put in a total line and it worked fine ever since. Just a bad one for whatever reason.

    If its wired right one line should be a direct hot line to the one side of the coil and the other through the lp control, safties
    for pumpdown. If the contactor isnt new and it pulled in before id be looking at corrosion, burns or something on the lp control contacts. Would have to be.

  13. #13
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    Quote Originally Posted by dangpgt97 View Post
    Did you add a new contactor? I had this happen to me on a siemens contactor brand new out of the box. Old contactor went out replaced with a new siemens and it wouldnt pull in for whatever reason unless i nuged it just a hair. Checked voltage and everything. Put in a total line and it worked fine ever since. Just a bad one for whatever reason.

    If its wired right one line should be a direct hot line to the one side of the coil and the other through the lp control, safties
    for pumpdown. If the contactor isnt new and it pulled in before id be looking at corrosion, burns or something on the lp control contacts. Would have to be.
    found some of them siemens contactors bad, the coil plastic melts and won't allow the contacts to close all the way. easy to pull it apart and visually see if that has happened
    If Guns Kill People, Do Pencils Misspell Words?

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    Before we work on artificial intelligence why don't we do something about natural stupidity?

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