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  1. #1
    Join Date
    Mar 2013
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    swan valley idaho
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    727

    r12 walk in to 134a

    so i looked at and old r12 walk in currently on 409. it has no t-stat or pump down solenoid just lp control. so i wanted to add t-stat and solenoid, but with 409 at 600 dollars a jug, cant justify buying it. may be a long long time until it all gets used. RSD suggested replacing condensing unit with a 134a unit, and then just use current txv and evap, add lls and stat. condensing unit and coil are both 10,000 btu, and looking at load calculations i should only need about 8,000 btu.

    so- with a good system flush, drier, and new condensing unit, does this sound like a decent plan? other thought was a 404a condensing unit, but unfortunately with the way the evap fits in this cooler i would have to take entire coil down just to replace txv because side access panels are blocked by cooler walls.

  2. #2
    Join Date
    May 2003
    Location
    Utah
    Posts
    733
    Why would RSD tell you to replace the condensing unit?

    Unless the compressor is dead, replace the oil and convert to R-134A. No need to replace the TEV. The TEV will have 20% more capacity with R-134A vs R-12, so make sure to check the SH setting.

  3. #3
    Join Date
    Mar 2013
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    swan valley idaho
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    727
    it's not that they are telling me that, it was a suggestion. basically like i say its controlled only by low pressure control. when it did shut off on control around 23 psi, it rose pretty quick back to cut in of 35 psi, so it seems suction valves aren't holding. i thought of putting a pump down solenoid and t-stat so it wouldn't short cycle on pressure control. with the cost of 409, and the fact the suction pressure isn't holding in off cycle, it seems like it may be time to replace condensing unit, and thought if i stick with 134 i could re-use coil and txv. of course these people are broke, so trying to avoid a complete new system. also it's a hermetic compressor.

    it is still cooling currently but can't think of how to stop short cycling without adding stat and solenoid. any other suggestion welcome. thanks

  4. #4
    Join Date
    Aug 2012
    Location
    willowick ,oh
    Posts
    261
    SPR, and cycle off of a tstat with a 5 deg swing

  5. #5
    Join Date
    Mar 2013
    Location
    swan valley idaho
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    727
    johnnyb- i should say without opening up system. (your suggesting suction pressure regulator right?). if i have to open up and loose any refrigerant i'm back to buying a 600 dollar jug of 409, which gets back to the original idea of just replacing condensing unit with 134 unit at that point.

  6. #6
    Join Date
    May 2003
    Location
    Utah
    Posts
    733
    Quote Originally Posted by kklobas View Post
    it's not that they are telling me that, it was a suggestion. basically like i say its controlled only by low pressure control. when it did shut off on control around 23 psi, it rose pretty quick back to cut in of 35 psi, so it seems suction valves aren't holding. i thought of putting a pump down solenoid and t-stat so it wouldn't short cycle on pressure control. with the cost of 409, and the fact the suction pressure isn't holding in off cycle, it seems like it may be time to replace condensing unit, and thought if i stick with 134 i could re-use coil and txv. of course these people are broke, so trying to avoid a complete new system. also it's a hermetic compressor.

    it is still cooling currently but can't think of how to stop short cycling without adding stat and solenoid. any other suggestion welcome. thanks
    23 psi = 23*F. What temperature is the box at when the unit cycles off at this pressure?

    35 psi = 38*F. It's not unusual that the pressure would rise to something close to this. A cylinder of refrigerant stored at 80*F ambient temperature will be a the pressure corresponding to an 80*F saturation temperature. Likewise, given the fact that the evaporator is partially filled with liquid refrigerant, as you're blowing the approximately 35*F refrigerated air in the box over the evaporator, the refrigerant saturation temperature will rise to something close to the box temperature, and the pressure will correspond to that saturation temperature.

    A time delay will prevent short cycling, but as you've already suggested the LLSV and TSAT would be a much better way to control the box temperature.

    Is the system short on refrigerant right now? If not, why are you concerned about adding refrigerant?

    Get a performance curve for that compressor and see if it is operating according to design specifications, rather than assuming that a rise in suction pressure where there is no pumpdown control is abnormal.

  7. #7
    Join Date
    Feb 2007
    Location
    Fremont, Indiana
    Posts
    1,556
    Why not spread the differential a little more and see if that helps tackle the short cycle? If it continues, then troubleshoot further before condemning valves

    sent from my Samsung Galaxy Note
    Member of the "Work Exchange Program"
    "Will work for knowledge"

    "Everyone is a genius. But if you judge a fish on its ability to climb a tree, it will live its whole life believing that it is stupid"
    A Einstein

  8. #8
    Join Date
    Sep 2002
    Posts
    12,568
    Just dump the mineral out the suction line, measure how much you took out, and put that much POE oil back in. Charge with 134 and adjust the SSH to about 18 at the compressor.

    For a 40 box set the operating control LP to about 34 lb. cut in and maybe a 15 lb. cutout. LEt it fly overnight and then maybe tweak the pressure control if you have to.

    PHM
    ------


    Quote Originally Posted by kklobas View Post
    so i looked at and old r12 walk in currently on 409. it has no t-stat or pump down solenoid just lp control. so i wanted to add t-stat and solenoid, but with 409 at 600 dollars a jug, cant justify buying it. may be a long long time until it all gets used. RSD suggested replacing condensing unit with a 134a unit, and then just use current txv and evap, add lls and stat. condensing unit and coil are both 10,000 btu, and looking at load calculations i should only need about 8,000 btu.

    so- with a good system flush, drier, and new condensing unit, does this sound like a decent plan? other thought was a 404a condensing unit, but unfortunately with the way the evap fits in this cooler i would have to take entire coil down just to replace txv because side access panels are blocked by cooler walls.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  9. #9
    Join Date
    Mar 2013
    Location
    swan valley idaho
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    727
    thanks everyone. PHM- why do you say 15lb cut out. thats only 12 degrees coil temp? it seems like it would freeze before then? i am concerned about the refer because to add solenoid i'll need to open system, and if i need any extra fefer after doing that, i dont have any.

    Can you elaberate on the time delay. specifficaly how it would wire in to the system?

    bunny- i'm with you that it wouldn't be abnormal to rise to 35 psi, just wandering how this thing could have ran for years with no t-stat or solenoid? original call i found coil froze solid,but pressure control was at 0psi cut out, 10 psi in, so that should explain the frozen evap.

  10. #10
    Join Date
    Feb 2007
    Location
    Fremont, Indiana
    Posts
    1,556
    Quote Originally Posted by kklobas View Post
    thanks everyone. PHM- why do you say 15lb cut out. thats only 12 degrees coil temp? it seems like it would freeze before then? i am concerned about the refer because to add solenoid i'll need to open system, and if i need any extra fefer after doing that, i dont have any.

    Can you elaberate on the time delay. specifficaly how it would wire in to the system?

    bunny- i'm with you that it wouldn't be abnormal to rise to 35 psi, just wandering how this thing could have ran for years with no t-stat or solenoid? original call i found coil froze solid,but pressure control was at 0psi cut out, 10 psi in, so that should explain the frozen evap.
    Would work like a constant cut-in control!
    Cut-in at 40 would act as defrost.
    You don't have 134a???

    sent from my Samsung Galaxy Note
    Member of the "Work Exchange Program"
    "Will work for knowledge"

    "Everyone is a genius. But if you judge a fish on its ability to climb a tree, it will live its whole life believing that it is stupid"
    A Einstein

  11. #11
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    Mar 2013
    Location
    swan valley idaho
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    727
    yes i have 134a its 409 i dont have.
    kramersoutdoor- what are you referring to? raising the cut in up more?

  12. #12
    Join Date
    Feb 2007
    Location
    Fremont, Indiana
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    1,556
    Quote Originally Posted by kklobas View Post
    yes i have 134a its 409 i dont have.
    kramersoutdoor- what are you referring to? raising the cut in up more?
    I believe phm was referring to changing system to 134.
    Setting cut-in at 40deg (as phm suggested) should keep coil from freezing
    Similar to using constant cut-in on a reach in
    sent from my Samsung Galaxy Note
    Member of the "Work Exchange Program"
    "Will work for knowledge"

    "Everyone is a genius. But if you judge a fish on its ability to climb a tree, it will live its whole life believing that it is stupid"
    A Einstein

  13. #13
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    Mar 2013
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    swan valley idaho
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    ok- yah that makes sense. i was wandering why you would let it run all the way to 15 before cutting out. thats a 12 degree coil, so i was thinking it would freeze before getting there.

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