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Thread: CPR's and EPR's

  1. #1
    Join Date
    Mar 2003
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    Greetings, I'm a newbie to the site and the trade. I'm seeking information on how to correctly set a CPR (Crankcase pressure regulator) and EPR (Evaporator pressure regulator valves).Kind of a how to. And any info on maybe what to avoid etc.. would be greatly appreciated.Thanks for your help and time. Scott

  2. #2
    Join Date
    Sep 2002
    Location
    South Dakota
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    6,579
    Originally posted by scootage
    Greetings, I'm a newbie to the site and the trade. I'm seeking information on how to correctly set a CPR (Crankcase pressure regulator) and EPR (Evaporator pressure regulator valves).Kind of a how to. And any info on maybe what to avoid etc.. would be greatly appreciated.Thanks for your help and time. Scott
    For starters, check this out;

    http://www.hvac-talk.com/vbb/showthr...threadid=25234

    There are a bunch of articles located in the "For Your Interest" area on the main page of this site. Scroll through them and you will locate lots of information on many topics.


  3. #3
    CPR--set for compressor load amps after defrost.

    EPR--set for the coil temp needed in that circuit

  4. #4
    Welcome to the group.


    We're pretty weird here. Hope you are too. That way, Dice wont have to pick on you too much. He picks on the new guys and scares off the kreeps!


    Setting a CPR valve ...hmmm.... Well ... you start out with a pair of pliers and you unscrew the cap on the end of the valve. If it has a cap, that is.
    Then you insert an allen wrench into the opening. If it has an opening to insert an allen wrench into. That is.

    Some use a plastic cap over the end and there is a bolt there to adjust using a wrench.

    The idea being, to adjust spring pressure to hold the valve back whenever the compressor is under full load during a start up.

    You want to use a CPR valve to prevent too much freon entering the compressor during start up especially after a defrost.

    CPR's are normally found on smaller units for low temp cases.

    Set the adjustment screw, bolt ... whatever .. so that when the unit comes back online, it does NOT draw over normal run amps.

    I like to bring down the case to temp then initiate a defrost.
    I dont leave the system in defrost for very long, just enough to heat things up a little.

    You could probably accomplish the same thing by using a portable tape deck and play back one of Kerry's old speeches.
    That oughta heat things up a Lot!!!
    Hot air does wonders to a refrigerated case!!! And John Kerry is FULL OF HOT AIR ... to be sure!!!

    But you've gotta be careful and select just the right Kerry tape to play inside your cabinet.
    Since Kerry is also full of ... shall we say ... "other elements" as well. And you certainly wouldnt want to contaminate the cabinet with these other elements! Since this would require you to also sanitize the case once you were thru heating it up.


    It may take a time or two of starting it up and amking adjustments before you feel you've got it right.

    Dont worry though, we all began right here where you are.

    It takes a pretty good man to aask a question, especially publically like this.

    We are proud to be a part of your education.
    Ask away.


    Oh ... and when you run into Diceman, ask him how Jack is doing.
    Then you might just want to join us in supporting this wonderful site.


    Oh .. and dont forget to make a friendly contribution to Diceman's favorite thread. It is called 9mm.
    We have all forten why he began that thread.
    And by now you'd think we might have progressed to at least 12 or maybe even 13mm by now.

    But no.... we're still @ 9mm and holding.


    Dave or Dow oughta be along any moment now and give you advice on your setting an EPR. Maybe ...just maybe .... good ol Icemeister will volunteer his method.



  5. #5
    Join Date
    Apr 2002
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    most of the time in the Philippines
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    1,211
    Good respones. My 2 pesos worth:

    http://www.sporlan.com Click on literature and start downloading and printing. If you're doing commercial refrigeration work, you need a Sporlan notebook on the truck.

  6. #6
    Join Date
    Jul 2000
    Location
    Guayaquil EC
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    10,259

    CPRs and EPRs..........

    I might as well jump in here too.

    The CPR's function is to limit the risein pressure downstream of the valve (hence the alternate terminology of CRO for close on rise of outlet). It's used commonly on single compressor low temperature systems to prevent motor overload during periods of initial pulldown and after defrost. As has been said, the best method is to get the system in one of these modes and set the valve to the rated load amps (RLA) of the compressor if it's a semihermetic (or hemetic) or to the full load amps (FLA) if it's an open drive unit.

    The EPR's function is to limit the rise in pressure of the inlet of the valve(hence the other term ORI). It's used widely on systems with multiple evaporators which operate at differing design pressures tied to a common compressor or compressors like in a parallel supermarket setup. The key here is to know what the individual evaporator's design condition is and set the EPR to maintain it. If it's not known, start with 10 Deg F (converted to psig) below the entering air temp of the evap coil when the load is at its desired temperature. The EPR is not typically used as the sole temperature control device, but more to keep an evaporator pressure close to design for stable performance.

  7. #7
    Join Date
    Feb 2004
    Location
    Medford Oregon
    Posts
    807
    Neither Sporlan nor Alco suggest using RLA to set CPR
    get a copy of their installation brochures

    a glance at a 9RS3-0675-TFC curve sheet will tell you
    why

    RLA is for fuse and contactor sizing - that's all

  8. #8
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    The Alco literature I just looked at said the best way to set a CPR to prevent motor overload during post defrost or pulldown is to measure motor amps. This to me is suggesting you use the maximum allowable running amperage rating for that compressor.....ie RLA.

    For some reason I can't get the Sporlan PDF to unzip and open for me so I have no commentary on that one.

    The purpose of the CPR is to prevent compressor motor overload. If your not setting the CPR to RLA, what value are you suggesting we use instead?

    I realize that the 9RS-0765 is a dual-rated pump (MT12/LT502) and a condensing unit manufactured with that model will have a RLA selected by the unit manufacturer (not necessarily Copeland) for the worst case condition which is probably the MT at its high end of the envelope. In that case you may not need the CPR in the first place.

    Is this what you were alluding to? Please enlighten us.

  9. #9
    Join Date
    Feb 2004
    Location
    Medford Oregon
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    maximum allowable rating on 9RS3-0675-TFC is below RLA
    RLA = 29.4
    MAX AMPS ON R12 CURVE IS 22.8

    RLA used to estimate amps is often way off
    especially in dual use compressors
    considering RLA in diagnosing problems oftem
    leads to wrong conclusions

    sporlan says
    "CRO's should be adjusted at start-up when the pressure in the evaporator is above the desired setting. The final valve setting should be below the maximum suction pressure recommended by the compressor or unit manufacturer."

    Alco says
    "the unit should be set on start up or after a defrost. the best method for checking for checking motor overload is to use an ampmeter on the motor leads during system startup or after a defrost cycle."




  10. #10
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    Jul 2000
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    Guayaquil EC
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    Originally posted by rocket
    maximum allowable rating on 9RS3-0675-TFC is below RLA
    RLA = 29.4
    MAX AMPS ON R12 CURVE IS 22.8

    RLA used to estimate amps is often way off
    especially in dual use compressors
    considering RLA in diagnosing problems often
    leads to wrong conclusions

    Sporlan says
    "CRO's should be adjusted at start-up when the pressure in the evaporator is above the desired setting. The final valve setting should be below the maximum suction pressure recommended by the compressor or unit manufacturer."

    Alco says
    "the unit should be set on start up or after a defrost. the best method for checking for checking motor overload is to use an ampmeter on the motor leads during system startup or after a defrost cycle."



    If you've got that compressor on an R12 system, It's not a low temp application and won't have or need a CPR valve.....so what's the point here?

    The Sporlan info states:

    "......The final valve setting should be below the maximum suction pressure recommended by the compressor or unit manufacturer."

    This is what I said about the upper end of the envelope....that's where they select the RLA for the unit.

    The Alco info says:

    "......the best method for checking for checking motor overload is to use an ampmeter on the motor leads during system startup or after a defrost cycle."

    That's what I said, too.

    Hey, rocket......I don't mean to get into a pissing' contest with you here my man, but what I said originally is and has been the generally accepted reason for installing a CPR and the method of setting one up.

  11. #11
    Join Date
    Feb 2004
    Location
    Medford Oregon
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    807
    9RS3-0675-TFC is Low Temp R-12
    at -40 it's amp rating is 15.2

    the only thing I wanted to clarify is that
    RLA is inaccurate for setting CPR's
    RLA can get you in the ballpark, but sitting
    in the dugout is much better

    as for the pissing contest, find a tech document
    by Copeland, Sporlan or Alco that says set CPR
    by RLA

  12. #12
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    Andy or Emerson.......any comment?

  13. #13
    Join Date
    Jan 2004
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    Earth
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    I have always used comp amps. If thats wrong, I would like to know.

    When I use Amps, they run like champs.
    A Diamond is just a piece of coal, that made good under pressure!

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