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  1. #1
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    Can an AC condenser coil bee too big?



    This is just a hypothetical question. If I took an AC unit with a small condenser and added a larger one or a second one, what would happen? Would it work? Or would the head pressure be too low for it to cool?



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    Re: Can an AC condenser coil bee too big?

    Condensers are sized for compressor rated output+ 10% for heat of compression....should ambient not exceed 48 degrees C. NB: Been a few years out of Domestic A/C Maintenance.

    Adding another condenser will destabilize a tried and tested system unless the original Condenser has severe Corrosion or is in a seriously high Ambient environment. The Basics is: Condense the refrigerant (change of state. Vapour to liquid ) and remove SOME sensible heat before expansion.

    Excess Cooling ( and i say that with respect to other members opinion on R.E...) has negative effects.
    Last edited by mikeref; 26-08-2016 at 09:38 AM.
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    Re: Can an AC condenser coil bee too big?

    Quote Originally Posted by mikeref View Post
    Condensers are sized for compressor rated output+ 10% for heat of compression....should ambient not exceed 48 degrees C. NB: Been a few years out of Domestic A/C Maintenance.

    Adding another condenser will destabilize a tried and tested system unless the original Condenser has severe Corrosion or is in a seriously high Ambient environment. The Basics is: Condense the refrigerant (change of state. Vapour to liquid ) and remove SOME sensible heat before expansion.

    Excess Cooling ( and i say that with respect to other members opinion on R.E...) has negative effects.
    Thank you for the response. How could more cooling have a negative effect? By making the head pressure too low?

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    Re: Can an AC condenser coil bee too big?

    Exactly over condensing is not good for any system,hence the reason for condensor fan speed control.

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    Re: Can an AC condenser coil bee too big?

    Putting a larger condenser on is not necessarily a show stopper. It does mean, however, that the airflow across it needs to be managed carefully or other controls such as bypasses need to be installed and controlled to ensure it doesn't over-condense. Over condensing brings the high side pressure down closer to the low side pressure. Expansion valves require minimum differential pressures to perform in a stable manner.

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    Re: Can an AC condenser coil bee too big?

    Quote Originally Posted by Scramjetman View Post
    Putting a larger condenser on is not necessarily a show stopper. It does mean, however, that the airflow across it needs to be managed carefully or other controls such as bypasses need to be installed and controlled to ensure it doesn't over-condense. Over condensing brings the high side pressure down closer to the low side pressure. Expansion valves require minimum differential pressures to perform in a stable manner.
    very true I have experienced the opposite many times where the evaporator is too big for the capacity of the condensor original post did say it was a hypothetical question but a very good post.

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    Re: Can an AC condenser coil bee too big?

    Quote Originally Posted by coolguy4 View Post
    Thank you for the response. How could more cooling have a negative effect? By making the head pressure too low?
    Lowering head pressure with a second condenser can cause a pressure drop between compressor discharge and the expansion Valve. Significant Pressure variation between these two points will turn the stable liquid flow at whatever pressure into a liquid / vapour mix. Vapour isn't going to do any work in the Evaporator.

    Seems both above^^ members weren't there when the term "Over Condensing" was discussed.
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    Re: Can an AC condenser coil bee too big?

    One more thing to take into consideration is the amount of refrigerant in the system.

    If you add an extra condenser, you will have to add refrigerant. Can the original compressor can handle it?

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    Re: Can an AC condenser coil bee too big?

    Paralleling 2 condensers the same size will actually reduce the pressure loss in the condenser. If they are piped in series(which would have to occur if they were dissimilar sizes) then yes, pressure drop becomes a major issue.

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    Re: Can an AC condenser coil bee too big?

    Besides pressure drop, if the condensers were installed in parallel, how would the overcooling cause a problem?

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    Re: Can an AC condenser coil bee too big?

    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

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    Re: Can an AC condenser coil bee too big?

    Wow. That link was nearly 6 years ago.
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    Re: Can an AC condenser coil bee too big?

    Hi coolguy4
    For some years we have installed condensers in series and in parallel for various reasons mainly heat recovery applications and mainly water cooled . These are carefully designed with control valves to control their function as these systems need to operate with larger refrigerant charges to satisfy the various functions as design
    Many larger systems have air cooled condensers which are made from 2 or more coil sections and are headered at the inlet and outlet, so are actually in parallel. Unless these condensers are piped correctly and the fans are controlled correctly then often liquid will back up in one condenser coil and the other condenser coil will pass saturated liquid/vapour out into the liquid line causing poor expansion valve control and poor cooling duties.
    But simply adding a secondary condenser coil into a system will need extra charge to keep a liquid plug at the outlet of the second condenser and as previously said the condensing pressure would need to be controlled to maintain sufficient p/d [pressure drop ] across the thermostatic expansion valve to the evaporator fully utilised. If you used electronic expansion valves then you could let the p/d drop to about 2 Bar as eev's can still function whereas the dumb Tev would not.
    So if you hyperthetically fitted a second condenser in parallel you need to pipe it correctly and still maintain sufficient p/d depending on expansion valve type
    Remember system components are selected at summer conditions with ambients of 35 Dec C + but controls on the fans must prevent the condensing pressure where ambients of minus 10 deg C or lower could cause over condensing to a point that would would cause the expansion valve to be unable to allow sufficient refrigerant into the evaporator and the coil to freeze and the plant to trip on its LP control
    Fitting a secondary condenser is not advised unless you fully understand what problems it can give you.
    Erratic condenser control using the R400 series of gases can cause fractionation and can lock the system out on high pressure fault

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