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  1. #14
    Join Date
    Nov 2009
    Location
    Richmond, working under tarps
    Posts
    918
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    Hvacnorth,

    If it were me, i would first test how the condensing unit reacts with the smallest load first.

    then test each load coming on line

    you have to think of all the possibilities

    without the ability of controlling compressor capacity, the ideal way, compressor life span may be sacrificed

  2. #15
    Join Date
    Sep 2002
    Posts
    25,163
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    Well; you couldn't leave the LPC set as it was before. <g> You would have to set it lower - to cut-out below the compressor's balance point with only the smallest evaporator active.

    As an EPR valve modulates, the downstream side (compressor-side) suction pressure will reduce. And to where you might ask? And the answer is: to whatever reduced compressor capacity which will exactly balance the heat loading coming from the evaporator.

    If you had an actual graphed compressor capacity vs suction pressure chart in front of you - you could pinpoint the exact suction pressure/compressor pumping capacity intersection.

    BTW: What do you mean with this statement:

    " . . . . setting a pressure control for r134a would basically guarantee lots of short cycling . . . "

    PHM
    ----------



    Quote Originally Posted by trippintl0 View Post
    In my experience with putting an EPR on a custom r404a prep table, the unit was running around 38 psi 5f SST, causing frequent ice ups. So I put the EPR at cond unit, set to about 54 psi 18f SST.

    I observed that as the box pulled down and EPR began to modulate, the suction pressure at compressor dropped down nearly to 20psi, which is much lower than it was before.

    Based on that I'm picturing the OP's cond unit might short cycle even worse with an EPR, although the coolers would run much better. I like IceMeisters idea of running a different gas, although setting a pressure control for r134a would basically guarantee lots of short cycling... I think we need a HGBP and desuperheating TXV too!

    Sent from my SM-G892A using Tapatalk
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  3. #16
    Join Date
    Jun 2019
    Posts
    2
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    EPR must be set before checking and setting Superheat on all three coils.

  4. #17
    Join Date
    Jun 2019
    Posts
    2
    Post Likes
    Generally epr valves are seen on rack systems with multiple circuits operating at different coil temps. This box electric defrost or air over defrost? If accumulator is used on the system then wire control circuit to shut system off instead of pump down when satisfied by thermostat or scheduled defrost. Assuming accumulator is there then use epr piped close to evap coils and use cpr close to compressor. Set cpr when box is warm to the RLA of compressor.

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