Page 6 of 6 FirstFirst 123456
Results 66 to 69 of 69
  1. #66
    Join Date
    Dec 2007
    Location
    East Coast
    Posts
    19
    Would just like to point out the amount of knowledge in this thread. I don't post as often as I should, but read this forum multiple times a week and for any tech that wants to be better this is the place to be. AR...happy you fixed the problem!

  2. #67
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,475
    Quote Originally Posted by icemeister View Post
    The superheat could still stand to be bit lower to around 4-6F. You'd be amazed at how much difference it can make. But be sure you're measuring the suction pressure at the coil and not at the compressor when you figure the SH because that couple of pounds of pressure drop in the suction line will throw you way off in a hurry at these temperatures.

    Your subcooling usually won't get much higher than what you've got simply because it's got a receiver in the system. There's no adjusting that with charge...or anything else. And yes, by definition at 3F SC you'll have a clear glass.

    Get it out of your head about altering the suction pressure by messing around with the expansion valve. It's not a pressure regulator...it's a superheat regulator.

    As for the nozzle question, we've already made a fix of sorts by upsizing the TXV capacity. This did one of two things. Either the nozzle was actually OK sizewise and the TXV was undersized...or the other way 'round. So at this point, unless you find you can't get the SH down to where you need it, I wouldn't be concerned about the nozzle sizing. The superheat is a major factor in telling you whether the coil is performing or not.

    The one thing which stands out here is the relatively high TD on the evaporator. You say the box is at 0F and the coil is at -20F SST, which gives a 20F TD. At design conditions it should be a 10F...but what are the design conditions for this job?

    By the numbers we have, the coil has a specific capacity of 9400 Btuh at a 10F TD and the condensing unit has a capacity of about 9400 Btuh at -20F SST and 90F ambient, so I'm assuming the system was selected for a -10F box temperature...correct?

    I think a lower superheat will help lower the TD and subsequently raise the suction pressure & lower the box temperature...but another 10F lower may be a push. Of course there may be other factors in play here.
    Yes im measuring pressure and temp at the evap. Ill drop the SH a few degrees. I know it is achievable. After the box got down to temp I adjusted the valve and went a little to far so can get it to 4 no problem.

    Good deal on the SC then.

    Yea I know the tev controls SH. With the smaller cartridge pressure was more of where I wanted it at around 8 or 10 psi but as already discussed, I couldnt get SH below 25 at the evap. I did have a colder box though..

    Glad I wont have to unbraze the valve and pull the nozzle.

    The box is in ambient conditions. That was accounted for when they sized it. They set it up for 115 degree ambient and a -15 degree box.

    Ill swing by monday and get the sh to 4 and see how it goes. Just seems like its struggling to maintain 0 and sub 0 temps and is running 24/7, except for three defrost cycles.

  3. #68
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,058
    Is there a pressure drop between the evap and the compressor?

    I know TXV's are not pressure regulators, But I have seen coils running proper superheat but overloading the suction line and raising the SST. had to increase superheats in order to reduce the load on the suction line to achive desired SST.

    It's rare, but I've seen it

  4. #69
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,475
    Havnt checked. Will surely take a look monday.

Page 6 of 6 FirstFirst 123456

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