Icing up due to overcharge? - Page 4
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  1. #40
    Join Date
    Apr 2002
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    11,808
    If I were to build an air conditioner from scratch, I would design it around a certain capacity and a certain ambient. You balance out the cooling coil and the compressor and come up with certain evaporating and condensing pressures.

    You look at the refrigerant pressure drop as it goes through the circuitting of the condenser coil, you subtract pressure drops of filter dryers, sight glasses etc in the liquid line, and you have less than the condensing pressure but more than the suction pressure.

    Downstream of the TX valve there is the pressure drop of the distributor, the distributer tubes and even the evaoprator coil itself.

    When you start subtracting all these in line pressure losses from the condensing pressure, and then subtract the evaporating pressure you are left with the pressure the TX valve has to work with.

    The TX valve must be capable of passing enough refrigerant flow based on this pressure differential.

    When there are no abnormal restrictions in the system, then over charging is just going to raise all the pressures.

    Suction pressure/temperature will go up, head pressure temperature will go up.

    I can't see the overcharge causing the freeze up.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

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  2. #41
    An overcharge can cause freezing, but it is a complicated scenario, typically it wont.It is more likely that it will freeze with a low or normal charge with other poblems such as airflow also being a factor.


  3. #42
    Join Date
    Mar 2005
    Location
    Toronto, Ontario. Canada
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    93
    I've got news for you guys. When you charge a system, you mainly keep your eyes peeled for compressor amps, suction pressure, head pressure and most important SUPERHEAT(SH). SUPERHEAT is calculated by SUCTION LINE TEMP(SLT) minus SATURATED SUCTION TEMP(SST). For high temp refrigeration(Air Cond.), a SH of in between 10F - 15F can be expected. Some systems are designed as high as 25F. In a capillary metering device system, as you add refrigerant, your superheat heat decreases. Since SST is approx 40F and if you begin to overcharge your SH decreases. This means that your SLT drops below 40F and if excessively overcharged, your SLT can easily reach below 32F.
    If there is excessive humidity in the ambient, thus air will lose its humidity onto coil and suction lines and compressor thus icing up due to SLT being below 32F.

    As far as a TXV system, overcharging will backup into condessor increasing head pressure eventually increasing RLA of both compressor and cond.fans. This will make one or the other or both shut off on overloads or if system is equiped with a high head pressure switch, it will shut AC down. The evap will be controlled according to SH as others have said.

    Therefore, yes you can ice up a system with an overcharge with a cap tube system only!

  4. #43
    Join Date
    Mar 2004
    Location
    Columbus Ohio
    Posts
    328
    I agree a system that is overchaged with "no other problems" will not freeze. The pressure would be elevated.
    Now low and med temp refrigeration is a different story...
    ofcourse the evap will freeze with overcharge.. and correct
    charge for that matter

  5. #44
    Join Date
    Mar 2005
    Location
    Toronto, Ontario. Canada
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    93
    Originally posted by ac/dc
    I agree a system that is overchaged with "no other problems" will not freeze. The pressure would be elevated.
    Now low and med temp refrigeration is a different story...
    ofcourse the evap will freeze with overcharge.. and correct
    charge for that matter
    Im assuming you didnt read what I posted. If you did you should re think your logic.

  6. #45
    Join Date
    Apr 2002
    Location
    Ann Arbor, MI
    Posts
    2,985
    Originally posted by airworx
    you guys are wrong however about how a txv works.
    if you overcharge a system that has a txv and we are not talking about an orfice. but a txv will close off to keep the superheat up to its setpoint say 15 degrees. as more refrigerant is added it will have to close off more and more to keep the superheat up and that will cause the suction pressure to drop.
    airworx, you're a bit confused a bit here. Let me help you out.

    Suction pressure is simply a function of heat load on the evaporator and your compressor/condenser capacity. If the TEV is operating properly, it will modulate refrigerant flow such that it will increase refrigerant flow into the evaporator at higher load conditions, thus raising suction pressure, and reduce refrigerant flow into the evaporatir at lower load conditions. This is due, of course, to the fact it controls superheat at the evaporator outlet. It does this function much better than a capillary tube or fixed restrictor.

    The key here is your heat load on the evaporator. It is the primary variable in determining your suction pressure.

    The TEV doesn't care about an overcharge system. It will continue to control superheat regardless. An overcharged system, however, will reduced your compressor's capacity and efficiency, which will cause higher than normal suction and discharge pressures.

    You might find the following of interest. http://www.sporlan.com/10-9.htm I wrote its original version


  7. #46
    chill factor

    THIS STATEMENT IS WRONG!!!

    This means that your SLT drops below 40F and if excessively overcharged, your SLT can easily reach below 32F. If there is excessive humidity in the ambient, thus air will lose its humidity onto coil and suction lines and compressor thus icing up due to SLT being below 32F.

    HOW IN THE WORLD IS THE COND. FAN AMPS GOING TO INCREASE!!

    increasing RLA of both compressor and cond.fans.


    AND YOUR CONCLUSION IS WRONG!!

    Therefore, yes you can ice up a system with an overcharge with a cap tube system only!

    This stuff is basic theory, how can you possibly not understand it. I can’t imagine how you troubleshoot refrigeration problems without understanding the basics. You guys that believe this better run back to the texts books, please.


  8. #47
    Airworx,

    I can’t believe that you’re sticking to your misguided line of logic. I could teach a monkey how a TXV or EXV works.

    What concerns me most is that you always are quick to give advice, and you don’t understand the basics.

    That’s like the blind leading the blind. You may have years of experience, which has given you some instinctive troubleshooting abilities, (troubleshooting without logic or understanding) that’s not enough, to advise or teach others.

    You know what a TXV does, but you don’t know how it does it.

    Many so called parts changing service techs work in the same manner, after changing enough parts it bound to get fixed.

    Understand, it’s you “who doesn’t understand refrigeration”, take a step back, listen and learn from the people here that want to teach you.

    The good thing about this thread is, a lot of the misunderstanding is being corrected.



  9. #48
    Join Date
    Mar 2004
    Location
    Columbus Ohio
    Posts
    328
    Chill Factor,
    Your right I didnt see your post before I posted. now that
    I have I think you might want to rethink YOUR logic.
    yes superheat will decrease on a overcharged cap tube sys.
    but suction pres will increase and the evap will be well
    above freezing temp. unless there is inadequate load on the evap coil. Then freezing would be caused by low load
    on evap...not overcharge. Explain how cond. fan amps increase in a overcharged txv sys.

  10. #49
    Join Date
    May 2004
    Location
    Caldwell, ID
    Posts
    395
    Originally posted by kerndt
    chill factor




    HOW IN THE WORLD IS THE COND. FAN AMPS GOING TO INCREASE!!


    Wondering about that myself.

  11. #50
    Join Date
    Mar 2005
    Location
    Toronto, Ontario. Canada
    Posts
    93
    Easy guys. The cond fan will rise in amps. It can or cant be a drastic rise. We're just getting into cooling season soon in Toronto. I'm still in the transition of heating to cooling.
    As i quickly think about it, the excess heat in condensor area will add to the amps of the motor while its operating. The motor depends on the air coming across it to cool it down. If that air is too hot, it will transfer into the motor. Heat travels from hot to cold.

    Have you ever noticed how hot a cond fan motor gets if cond is plugged. Yes i know that the static also has something to do with it, but so does the ambient temp coming across the motor.
    I hope you guys see how the compressor amps will go up in a TXV!

    [Edited by chill factor on 04-09-2005 at 09:50 PM]

  12. #51
    Join Date
    Mar 2005
    Location
    Toronto, Ontario. Canada
    Posts
    93
    AC/DC

    Your thinking about inside the system. If your SLT is dropping dont you think the surrounding air has a dewpoint which will condense on the lines. If SLT and I repeat SLT is below 32F regardless of ref pressure that condensation will form ice!

  13. #52
    are you guys deaf. i said a refrigeration system and the exv on a flotronic chiller. i did not say an air conditioner.

    also when you overcharge a system head does go up but on a txv system the tx bulb senses temp not pressure and as the temp drops the pressure in the bulb drops the spring and evap pressure overcome this pressure and pinch off the valve
    which causes the suction pressure to drop.
    now i know theres someone out there that knows how this thing works because you guys apperantly do not.

    i think this is the commercial posting if not im sorry.

    [Edited by airworx on 04-10-2005 at 10:37 AM]

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