Page 3 of 6 FirstFirst 123456 LastLast
Results 27 to 39 of 67
  1. #27

    and...?

    low load: low suction, low superheat, normal head ?

    and on the condense no condense argument, I'm still waiting to hear if this was the biblical flood. Sounds like the result wasn't stable, was the TEV searching? At least during the time the suction was down at 30 psi with a temp of 16 there was superheat. So that shouldn't have been a flood, just icing back because of low refrigerant return temps. I'm waiting for HVAC689 to describe the fluctuating pressure characteristics and any range of temps observed.

    maybe there really is no such thing and changing water through two phases on the suction tube really always means boiling refrigerant, ergo no superheat almost by definition, but at least according to the initial report it was cold refrigerant temp, not lack of superheat.

    I'm thinking that blocked distributor tubes would duplicate a multiple symptom problem, both low load and meter restriction, because if the design is for 4 pipes through the evap, having only 1 of those open has to cause an additional pressure drop. Even if the TEV were all the way open it probably couldn't overcome that 'design change'.

    Brian

  2. #28
    Join Date
    Jun 2004
    Location
    Olean, NY
    Posts
    1,446
    Quote Originally Posted by aceinstaller View Post
    after rereading your post green ears,


    you had all 100% of the load you needed, but had a lack of refrgigerant in the coil causing it too pick up too much heat. the restriction caused the low pressure, and the high load caused the high superheat.
    Thanks for taking the time to help man, seriously. But I really need to change my username

    He has a full load too (warm air). Weather the system is overly metered at the TXV, or at the distributer tubes, or at the drier three inches before the TXV, the result is still the same....not enough refrigerant in the evap (to absorb the load as sat vapor) and therefore high superheat. He has a full load, but only 25% of the refrigerant needed in the evap.

    I realize that condensing means turning gas to liquid. One poster said that of you arent picking up superheat in the evap, you probably dont have any subcooling. I have to be misunderstanding the comment he made. Or I am misunderstanding the original posters situation.

    If his evap has enough air, with restricted refrigerant, he should have high superheat low pressure gas. With the refrigerant backing up in the condenser, and low load on the refrigerant system, the refrig should be stacking in the condenser and subcooling.
    Guinness for strength

  3. #29
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    Quote Originally Posted by archibaldtuttle View Post
    I'm thinking that blocked distributor tubes would duplicate a multiple symptom problem, both low load and meter restriction, because if the design is for 4 pipes through the evap, having only 1 of those open has to cause an additional pressure drop. Even if the TEV were all the way open it probably couldn't overcome that 'design change'.

    Brian
    The blocked distributors tubes do not represent a meter restriction.

    The best analogy for 3 blocked distrbutor tubes out of 4 on a 5 ton evaporator is you've replaced a properly working 5 ton evaporator with matched TEV with a 1.25 ton evaporator controlled by a 5 ton TEV.

    You will run low suction pressures and your TEV control won't be very good. You won't starve, and you will more than likely have flooding problems.

  4. #30
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720
    Quote Originally Posted by Andy Schoen View Post
    The blocked distributors tubes do not represent a meter restriction.

    The best analogy for 3 blocked distrbutor tubes out of 4 on a 5 ton evaporator is you've replaced a properly working 5 ton evaporator with matched TEV with a 1.25 ton evaporator controlled by a 5 ton TEV.

    You will run low suction pressures and your TEV control won't be very good. You won't starve, and you will more than likely have flooding problems.
    What!
    You're saying a 1.25 ton net capacity evaporator will flood back to a 5 ton compressor?
    Isn't the low suction pressure caused by a lack of sufficient quantity of refrigerant to the compressor? How could it flood then?
    jogas

  5. #31
    Join Date
    Jun 2004
    Location
    Olean, NY
    Posts
    1,446
    Quote Originally Posted by Andy Schoen View Post
    The blocked distributors tubes do not represent a meter restriction.

    The best analogy for 3 blocked distrbutor tubes out of 4 on a 5 ton evaporator is you've replaced a properly working 5 ton evaporator with matched TEV with a 1.25 ton evaporator controlled by a 5 ton TEV.

    You will run low suction pressures and your TEV control won't be very good. You won't starve, and you will more than likely have flooding problems.
    Now I get it.
    Guinness for strength

  6. #32
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    Quote Originally Posted by greenears View Post
    Now I get it.
    I'll let you explain to jogas.

  7. #33
    Join Date
    Jun 2004
    Location
    Olean, NY
    Posts
    1,446
    If you have 1/5 the evaperator, you need 1/5 the TXV. Now if I could just understand what Griff meant by saying it can't condense....

    I mean, even if it comes back liquid and superheats in the compressor, it's gonna pressurize and cool to a liquid. It's prolly going to spent a ton of time in there and subcool too......
    Last edited by B_roche; 06-21-2008 at 07:06 PM.
    Guinness for strength

  8. #34
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720
    Quote Originally Posted by Andy Schoen View Post
    I'll let you explain to jogas.
    I'd rather hear it from you.
    You're saying a tube that is 1/5 the required total feeder size is going to push thru enough refrigerant to a compressor that has 5 times the pumping capacity. The suction will be low, but it can flood back.
    Are you thinking of a TEV's (in)ability to throttle down under low load conditions? If so, we do not have that condition here. We have 5 tons of air going across an evaporator that is only 1/5 full of refrigerant, that is going to a compressor that is pumping at a rate of 5 tons. That's what is causing the low suction in the first place.
    What am I missing?
    jogas

  9. #35
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720
    Quote Originally Posted by greenears View Post
    If you have 1/4 evaperator, you need 1/4 TXV. Too much volume will get through.
    How will it get thru. You've got almost all of your tubes plugged with no compressor capacity reduction?
    jogas

  10. #36
    Join Date
    Jun 2004
    Location
    Olean, NY
    Posts
    1,446
    Quote Originally Posted by jogas View Post
    How will it get thru. You've got almost all of your tubes plugged with no compressor capacity reduction?
    jogas
    I thought that was Andy who posted that....I'm in no position to teach lol that was a joke obviously. You'd still have entirely too big of a compressor with entirely too big of a TXV. I actually cant remember the effect of an oversized TXV. I had a sporlin class where they explained it but I'm at a loss now. I do believe that it becomes a volume issue...maybe a velocity issue though which actually makes more sense
    Last edited by B_roche; 06-21-2008 at 07:16 PM.
    Guinness for strength

  11. #37
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720
    Quote Originally Posted by greenears View Post
    Too much will get through the one remaining open tube
    But that refrigerant will be flashing (evaporating) in the suction line due to the imbalance between evap and compressor. That's where you think you're flooding, but you're not really. The TEV bulb is trying to compensate for the blocked tubes, but can't.
    Did you check the compressor discharge temperature? If so, what was it?
    jogas

  12. #38
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    Quote Originally Posted by jogas View Post
    I'd rather hear it from you.
    You're saying a tube that is 1/5 the required total feeder size is going to push thru enough refrigerant to a compressor that has 5 times the pumping capacity.
    Yes.

    Quote Originally Posted by jogas View Post
    Are you thinking of a TEV's (in)ability to throttle down under low load conditions?
    That's part of the problem.

    Quote Originally Posted by jogas View Post
    If so, we do not have that condition here. We have 5 tons of air going across an evaporator that is only 1/5 full of refrigerant,
    We have 5 tons of air flow across the evaporator and about 75 percent of it is missing the mark... It is flowing across tubes with no refrigerant in them.

    Quote Originally Posted by jogas View Post
    We have 5 tons of air going across an evaporator that is only 1/5 full of refrigerant, that is going to a compressor that is pumping at a rate of 5 tons. That's what is causing the low suction in the first place.
    That is correct. But even with my analogy, a 1.25 ton evaporator that is attempting to cool the 5 tons of air properly (say 2000 CFM), you would have very high TDs resulting in very low suction pressures. Compressor capacity would drop from 5 tons to perhaps around 3 tons. The TEV is way oversized in either case. Blocked distributor tubes will not cause the TEV to control at high superheat, unless all of the distributor tubes are blocked.

  13. #39
    Join Date
    Jun 2004
    Location
    Olean, NY
    Posts
    1,446
    .
    Last edited by B_roche; 06-21-2008 at 07:37 PM.
    Guinness for strength

Page 3 of 6 FirstFirst 123456 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