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  1. #14
    I would agree that an overcharge would raise suction pressure and SST. I do not believe an overcharge will cause icing up like you will see with an undercharge.

    Low airflow is another story but that is nothing to do with the charge.

  2. #15
    you dont know refrigeration or txv operation then. because an overcharge will put more liquid in evap which causes a lower line temp which will close the txv off which will lower the pressure which will lower the temp which will cause frosting. if you dont belive then the next time you work on a 35 degree box overcharge to 30 or 40 degree subcooling and watch.

  3. #16
    I don't think you know which way is up.

    I never meant any disrespect.

    Look at all the other posts on this thread.
    I don't believe anyone agrees with you. Call sporlan tech support, at the factory, maybe they can inlighten you.

  4. #17
    Join Date
    Apr 2004
    Posts
    7,680
    Many times a improperly operating TXV, mismatch or other restriction can lend itself to being overcharged in an attempt to get the pressures up by a less than thourough technician... So, yes an overcharged system can freeze but the root cause is the restriction.

  5. #18
    im sorry you dont understand the refrigerant system.

  6. #19
    Join Date
    May 2003
    Location
    Charleston SC
    Posts
    123
    If you are freezing a coil on a direct expansion air conditioning system, the more likely culprit is a lack of air flow.
    When there is not enough volume (cfm) across the evaporator coil there is not enough heat to boil off the refrigerant fully and add superheat to the vapor so the refrigerant temp drops. Normally we have about 40-45 degree F. refrigerant temperature in an air conditioning coil.
    There are other conditions that can cause icing of the evap coil, such as the condensing temperature being too low. This can happen for example if we are running a condensing unit with no low ambient controls with an outside air temp say 40 F. Our condensing temperature instead of being 100 F drops to 50 or so. After this 50 degree refrigerant goes through the metering device, our refrigerant temperature in our evaporator is suddenly below the freezing point of water >32 F.

    So if you are freezing a dx airside coil, it is probably not from an overcharge of refrigerant.

    Regards

    Coolairman

  7. #20
    Join Date
    Nov 2004
    Location
    up in the hizzy
    Posts
    1,407
    The TXV allows refrigerant into the evaporator by sensing the temp of the succion line(superheat),with high superheat the temp. of the sensing buld icreases and so does its opening pressure,In a externally equalized txv the opening pressure inside the bulb fights the closing pressure of the succion line (equalizer) and the pressure of the spring.
    A high subcooling (Overcharge,low ambient temp.) will not iced up the evaporator coil.
    correct me if I'm wrong!



  8. #21
    Valdelocc

    Well said,
    I feel like Im beating a dead horse, on this issue. Equalization is accomplished either internally or externally depending on the valve design, and like you said, it counters the sensing bulb pressure to help maintain a proper superheat.

    Even the electronic expansion valves operate by the same logic. Suction pressure, (not liquid presence) and temperature, equals superheat. These are measured by a suction line transducer and a coil temperature sensor; the controller can open or close the EXV on these measurements and maintain a proper superheat. High pressure, sub-cooled liquid or low pressure, will have effects on the valve trying to maintain superheat, but only in super extreme cases, could it cause an iced up evaporator. Like many have said, it was not the overcharged condition that directly caused the problem.

    I think airworx just wanted to put his two cent in, and it ended up costing him two dollars.


  9. #22
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Well,

    This is basic theory guys.

    The question, the only question being asked is "will a system ice a coil if overcharged".

    No. Not by itself.

    As the refrigerant flashes into the coil out of TXV we got some vapor and liquid. If we apply heat we boil the liquid off absorbing heat. If there is too much liquid, we will never boil it off. If we don't, how does latent heat of evaporization take place?

    If the heat aint going through the pipe, no condensation will form. If you can't absorb the heat, you can't form condensation on the outside of the pipe. Heat transfer must take place for this condensation to form. Then on top of that, If you do absorb heat, the sst, or rather refrigerant temp must be below freezing too.

    Airworks, your being very cocky while showing a lack of knowledge.

  10. #23
    Join Date
    Sep 2002
    Posts
    1,389

    But wait!

    Fixed orifice:

    Evaporator running at 25 degrees for whatever reason (low air flow but with a sufficient system charge and at balance point) and five degrees superheat. Refrigerant is added, to bring up the suction pressure. The added charge further reduces the suction line refrigerant temperature. Does the line freeze at 28-29 degrees while adding charge before it conceivably tries to come up to say 30 degrees?

  11. #24
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    twopipes, I like the way you think. An overcharged fixed orifice system will lower suction line superheat or cause a flooding condition. But it will also raise suction pressure. You need to somehow argue that overcharging a unit somehow reduces suction pressure.

    Granted, overcharging a fixed orifice system may well improve evaporator coil performance, and this could be beneficial if you are not flooding back. And over time, improved evaporator coil performance may allow you to operate at lower suction pressures. But then are you really overcharged, or do you simply have the proper charge for optimal evaporator coil performance?

    With a TEV system, if the TEV is properly controlling superheat, then coil performance is effectively fixed. Suction pressures will go up or down based on the load on the evaporator. Overcharging such a unit will do nothing other than resulting in higher suction and discharge temperatures and making your compressor less efficient.

  12. #25
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    I don't follow what you guys are saying.

    My point is, heat tranfer needs to take place in order for condensation to form, then ICE.

    You only get that with latent heat of evaporization.

  13. #26
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    Originally posted by Dowadudda
    I don't follow what you guys are saying.

    My point is, heat tranfer needs to take place in order for condensation to form, then ICE.

    Dow, your thinking is ok. For condensation and ice to form, you need low suction pressures, less than the equivalent of about 26F on a typical a/c evaporator coil. The problem with the ice formation due to overcharge theory is how do you get low suction pressures.

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