Page 3 of 4 FirstFirst 1234 LastLast
Results 27 to 39 of 43
  1. #27
    Join Date
    Mar 2004
    Location
    Las Vegas, Nevada
    Posts
    1,647
    Yep. Freezers want 3-6 deg of S/H.Usually.
    The views and opinions posted here are my own. They do not reflect the corporate policies of my employer and will most likely get me fired at some point.

  2. #28
    Join Date
    Sep 2010
    Posts
    69
    OK then 20-25 deg superheat at compressor. I am confused at the 6 deg at the evaps than was recommended and then 20-25 at the compressor. I guess maybe I should check the total tonnage of the compressors and the evaporators to make sure they are correct size. There is one solenoid valve to shut off liquid line to all three evaps. From what I could see on the short time I was there, the compressors come on when the solenoid energizes and the pressure rises. The compressors go off when tstat satisfies and closes the solenoid for pump down. No unloaders.

  3. #29
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,563
    Quote Originally Posted by icemeister View Post
    I know you meant to say, "...no less than 20F SH...".
    Yes, you caught me.

    Quote Originally Posted by OhioTech View Post
    OK then 20-25 deg superheat at compressor. I am confused at the 6 deg at the evaps than was recommended and then 20-25 at the compressor. I guess maybe I should check the total tonnage of the compressors and the evaporators to make sure they are correct size. There is one solenoid valve to shut off liquid line to all three evaps. From what I could see on the short time I was there, the compressors come on when the solenoid energizes and the pressure rises. The compressors go off when tstat satisfies and closes the solenoid for pump down. No unloaders.
    I'll take this time, though, to say that a cold compressor is a happy compressor.

    Taking "no less than 20" to it's logical end, we could easily run 50-60-80 plus superheat at the compressor. Not difficult to see on a low temp unit, really.

    No less than 20, but, IMO, not much more than 30-40 degrees SH at the compressor.

    The 3-6 at the evaporator and 20 at the compressor really come into play when you see a longer or an uninsulated suction line.

    300+ feet of suction line can add quite a bit of superheat to a system, even if it is insulated.



    Set the SH at the evaps, then check it at the compressor and see how it is. Depending on system operation and conditions, you MAY need to tweak the evap SH up a bit to get SH at the compressor, which is your overriding concern.





  4. #30
    Join Date
    Sep 2010
    Posts
    69
    I would say the suction line is 100-125ft insulated untill it gets to the accumalator. Accumalator is a ball of ice.The compressor that has failed is thr first one after the accumalator. I will check the superheat in the full load, both compressors running.

  5. #31
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,563

  6. #32
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    1,439

    Very Important

    Lots of people rush to adjust superheats.

    Wait til the system is at its normal operating temperature for a day at least.

    Also make damn sure all the defrost heaters are working as they should.

    Also verify crankcase heat function. Almost sounds like bearing washout from diluted oil.


    See any foam?

    Also, when compressor was changed, is the piping the same? the compressor the exactly same? If not, one compressor may be getting more mass flow then the other.

    Balance is absolutely critical.

  7. #33
    Join Date
    Mar 2011
    Location
    East Coast FL
    Posts
    1,058
    Some really good suggestions have been made, would like to add a lil about the comp sh.

    20* is a great number across the board, you could see a lil less if your evap is close coupled, nothing to be too concerned with if everthing is running right. (in general)

    Anything higher than 20* at the compressor could be a problem - depending on your SST. 40* to 60* comp sh on a low temp system with a -10* SST and 30* to 50* suction gas temp would be fine. Plenty of motor cooling there.

    On the other hand 40* comp sh on an a/c system with a 40* SST would give you 80* return gas and the compressor motor would not be happy if that were to continue for any length of time.

    Just something to think about.

    Not that you have much control over the actual gas temp entering the compressor, its usually not a big problem if the evap sh is inline.

    Someone mentioned CCH, those things go out all the time and they are very important for a recip comp. I have seen current sensing switches installed on the CCH line and wired into the CC control circuit.

  8. #34
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,563

  9. #35
    Join Date
    Sep 2010
    Posts
    69
    Central Ohio

  10. #36
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,563
    Quote Originally Posted by OhioTech
    Central Ohio
    Little far.

    If you were closer to Northeastern OH, I'd offer a cuppa joe and a chat about your unit.

  11. #37
    Join Date
    Mar 2004
    Location
    Las Vegas, Nevada
    Posts
    1,647
    Once upon a time, I figured out that a respected voice on HVACTalk, Marvin, lives here locally in my part of the world. Thats led to any number coffees, a few breakfasts, a few lunches. Every one of those visits has left me just a little bit more smarter. OhioTech, JPSmith1cm is another of HVACTalk's respected voices. Even if you've got your current problem solved, gas up the rig and go have that coffee.

    Just my two cents.
    The views and opinions posted here are my own. They do not reflect the corporate policies of my employer and will most likely get me fired at some point.

  12. #38
    Join Date
    Apr 2012
    Posts
    36
    Quote Originally Posted by OhioTech View Post
    New compressor vibrating badly,low oil pressure.Oil is grey and full of metal. Shut unit down.They have common suction/discharge,an oil seperator,henry oil Thanks
    newbie here, common suction? How is the oil separator piped and is the oil pressure switch wired correctly? Unloading? Staged? Pump down or selinoid drop? Just thinking out loud.

  13. #39
    Join Date
    Mar 2004
    Location
    Las Vegas, Nevada
    Posts
    1,647
    Quote Originally Posted by Senior1 View Post
    newbie here, common suction? How is the oil separator piped and is the oil pressure switch wired correctly? Unloading? Staged? Pump down or selinoid drop? Just thinking out loud.
    http://www.sporlanonline.com/110-136_012002.pdf
    The views and opinions posted here are my own. They do not reflect the corporate policies of my employer and will most likely get me fired at some point.

Page 3 of 4 FirstFirst 1234 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event