Page 11 of 12 FirstFirst ... 456789101112 LastLast
Results 131 to 143 of 151
  1. #131
    Join Date
    May 2002
    Location
    Madison, Wisconsin
    Posts
    430
    Originally posted by Dowadudda
    ... latent heat of evaporization.
    Nicely mangled!
    My compliments.
    This message was packed by weight, not by volume.
    Some settling of the electrons may have occurred during shipping.

  2. #132
    Join Date
    May 2002
    Location
    Madison, Wisconsin
    Posts
    430
    Let me fling a scenario out here that might explain what a little of the confusion might be about.

    Medium temp refrigeration seems to be Airworx test-bed of choice... so...

    We carefully select a medium-temp box. Typically, the evaporator runs below freezing. Typically, there is no defrost timer, heater, etc. The evaporator, to keep from freezing up, depends upon staying in the off-cycle long enough between cycles that the 34* air blowing through the coil can defrost it.

    Now lets say that someone conspires to get the evaporator over-fed. Maybe it's a cap tube system, and someone overcharges it. So the overfed evaporator's temperature goes up, both from the extra refrigerant in the evaporator, and because the compressor is straining against the over-fed condenser and can't pump as well. Hopefully we can all agree that the evaporator temperature will go up.

    So the run cycles get longer, the time between cycles gets shorter. Though the evaporator is warmer, it is still below freezing, and now capable of building a little extra ice every cycle. If the off-cycle gets too short, the coil may not defrost completely. Which could lead to the coil icing up.

    That said, I would never expect this to happen in an expansion valve system from an overcharge. And, even in this egg-zample, when the unit is overcharged, (I hope we all agreed on this, above) the evaporator temperature goes up, not down. Such a freeze-up would probably have to be abetted by something like an under-sized or dirty evaporator as well.

    But I can just barely buy the idea that, under just the egg-zact right conditions, there might be a properly-charged medium temp system (but only with a fixed egg-spansion device!) that could seem like it functioned sort of normally - but might just freeze up if the charge was increased just the right amount.

    Theoretically.
    This message was packed by weight, not by volume.
    Some settling of the electrons may have occurred during shipping.

  3. #133
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    The interesting aspect of arguing theories as to why certain things happen is you never really know if it fits all of the observable facts, unless the one presenting the issue is quite detailed in their explanation.

    If the theory does fit all of the observable facts, then it is simply a matter of applying Occam's razor (alternatively known as the KISS principle). Is it the simplest explanation that fits the observable facts?

  4. #134
    Join Date
    May 2002
    Location
    Madison, Wisconsin
    Posts
    430
    Originally posted by Andy Schoen
    The interesting aspect of arguing theories ... is you never really know if it fits all of the observable facts, unless the one presenting the issue is quite detailed in their explanation.

    If the theory does fit all of the observable facts, then it is simply a matter of applying Occam's razor (alternatively known as the KISS principle). Is it the simplest explanation that fits the observable facts?
    Agreed.

    Einstein has an amusing re-statement of Occam's Razor that goes much like, "Things should be as simple as possible, but no simpler." People argue about whether he was referring to theories, science education, or life in general.

    Unfortunately, we didn't start out this thread with very many facts. That makes it much easier, and perhaps more tempting, to theorize. However, a few theories in this thread defied facts such as the laws of physics... that we know, hopefully, even if they weren't stated in the opening post.

    I set out the scenario above in part because, in my experience as a refrigeration guy, I thought I had seen this very thing happen once - to my surprise at the time. I was called to work on a frozen system, thawed it out, and got it running. As the the box temp was normalizing, I realized that the unit was overcharged, and removed some refrigerant. When the box got fully down to temperature, I removed a little more. It's tempting to say, "Result: it didn't freeze up." But I'm not that confident that it's failure to freeze up again wasn't because of some other cause. So I've never wanted to make the cause/effect connection. Yet, thawing it out and removing refrigerant were the only things I did to "fix" the problem.

    I wasn't in a position, at the time, to recreate the exact situation and test the theory. And because attempts at recreating the situation on other systems failed, I've always wondered whether it is actually possible to have this situation: Adding refrigerant to a medium-temp system that's running reasonably well induces it to freeze.

    So I'm hoping someone can confirm the theory, or shoot it full of well-placed holes.

    [Edited by fixitman on 05-14-2005 at 03:18 PM]
    This message was packed by weight, not by volume.
    Some settling of the electrons may have occurred during shipping.

  5. #135
    Join Date
    May 2004
    Location
    Los Angeles, CA
    Posts
    1,560

    What was "fixed"??????

    Dear Fixitman,

    Regarding your previous post:

    “Yet, thawing it out and removing refrigerant were the only things I did to "fix" the problem.”

    Based upon your statement of: “But I'm not that confident that it's failure to freeze up again wasn't because of some other cause.” I can only conclude that your “fix” of the problem might of merely have been the temporary elimination of a symptom, rather than the root cause, of the original problem my friend.

    Lastly, if you carefully read the “original posted question” that started this thread it stated an “A/C unit” rather than a medium temperature refrigeration unit.

    But I have to agree with you 100% in the fact that expanding the original question to involve, and discuss theories from the full spectrum of the A/C and refrigeration sector is a great, and informative learning forum.

    Respectfully Submitted,
    John J. Dalton

  6. #136
    Originally posted by Andy Schoen
    No doubt it is possible to overcharge a system and have insufficient airflow and create ice, all else being correct with the system. With a fixed restrictor system, the overcharge will cause floodback, and the overcharge cannot be so great as to cause suction pressures to be greater than say about 50 psig on R-22 if one expects ice to form. If a tech is mistakenly charging a system to overcome low airflow, however, he will typically charge the unit to a more reasonable suction pressure, 60+ psig, resulting in no ice formation, and greater floodback.

    A system with a TEV will behave similarly, though the TEV should prevent floodback as it would control superheat.

    As john dalton points out, however, the problem here is low airflow. The overcharge is not the cause, but simply the result of a mistaken attempt to resolve the insufficient airflow problem.




    That's the one that finally nailed it

  7. #137
    Join Date
    Jan 2006
    Posts
    5

    Confused

    Ive got one for you guys. But this is the AC in a 95 mazda pickup.

    I gave it a small shot of Hot Shot Freon and it started cycling at close to 30 PSI.

    I charged it up to about 45-46 PSI ( Reccommended for cars) low side because it was NON running AC. It now works but she says it is too cold . After about a hour of running and shutting the fan down to a lower speed it doesnt cool as good.

    After I checked it out after 40 mins of Idling on HI speed the suction line sweats and Ices all the way up to the compressor, Im guessing the evaporator coil is too, and makes me think that it is overcharged. But my new low side reading is 35-40 PSI though and I dont have the right high side gauge for R12 on cars.

    HELP

    Sorry For bringing this one WAY back from the dead too!

  8. #138
    Join Date
    May 2002
    Location
    Madison, Wisconsin
    Posts
    430
    Sounds like low air flow to me: dirty evap coil, rat in duct, etc. However, if the suction goes too low on auto AC, there is a "superheat switch" (or whatever they're called this week) that's supposed to shut the compressor down in just this situation. Sounds like that's not working, and your compressor may be in danger of drowning. The system might be overcharged as well.

    You're swimming in some pretty deep water here, knowledge-wise. I suggest you have it checked out by someone who knows how it works before your compressor needs a funeral.
    This message was packed by weight, not by volume.
    Some settling of the electrons may have occurred during shipping.

  9. #139
    Join Date
    Apr 2005
    Posts
    517
    I cant believe what I am reading????

  10. #140
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    439
    Quote Originally Posted by zz502 View Post
    Ive got one for you guys. But this is the AC in a 95 mazda pickup.

    I gave it a small shot of Hot Shot Freon and it started cycling at close to 30 PSI.

    I charged it up to about 45-46 PSI ( Reccommended for cars) low side because it was NON running AC. It now works but she says it is too cold . After about a hour of running and shutting the fan down to a lower speed it doesnt cool as good.

    After I checked it out after 40 mins of Idling on HI speed the suction line sweats and Ices all the way up to the compressor, Im guessing the evaporator coil is too, and makes me think that it is overcharged. But my new low side reading is 35-40 PSI though and I dont have the right high side gauge for R12 on cars.

    HELP

    Sorry For bringing this one WAY back from the dead too!
    Got one question for you, when you added the "hotshot", did you recover the remaining refrigerant prior to adding the "hotshot"?

    From what I've been told, thats only supposed to be added to a system thats been recovered and evacuated.
    When you do a job, Always make it easier for the next guy, because you may be the next guy working on it.

  11. #141
    Join Date
    Oct 2007
    Location
    Huntsville, AL
    Posts
    406
    When people ask me what caused there suction line to freeze up I always tell them it is because the suction line is below the dew point and below freezing. I also just realized this is a 2 year old post but I have already typed all this so I am bumping it...lol

  12. #142
    Join Date
    Jan 2006
    Posts
    5
    I would have to guess this is the shallow end of the knowledge pool. I couldnt even remember posting this until it popped up into my email today! This one turned out to have a hairline crack in the suction line. And a dirty cabin air filter. They would run the ac at the coldest setting when it wouldnt keep up. Freezing the Evap and then No cooling. At the time, it had been evacuated, put in a vacuum and already been charged with 414b.

  13. #143
    Join Date
    Jun 2008
    Posts
    73
    Why does refrigeration keep coming into this?

    under, over, correctly charged, a 40deg boxes coil is going to ice up no matter what. Which is why it must have at the least a off cycle defrost.

    oh never mind this is 4 years old and someone already pointed this out

Page 11 of 12 FirstFirst ... 456789101112 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