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Thread: changing orfice

  1. #14
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    Nov 2000
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    Quote Originally Posted by mrlighturfire View Post
    I always change everything from indoor coil from line set with a new condenser. In my opinion it avoids call backs and everything is matched up correctly. Not sure about goodman but I know Lennox for sure still uses orifice.
    Goodman does use orifice metering on 13 and some 14 SEER systems. So does Carrier.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  2. #15
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    Quote Originally Posted by bobb25 View Post
    If you have an owner that’s SO cheap that he doesn’t want a TXV, then IMO, walk away from the job. If you REALLY need the work, then CYA. Make sure you write in the contract something like “recommend changing inside coil” and “no warranty on labor”.

    Straight air is pretty forgiving, and you shouldn’t have any trouble, at least for the first year, especially if you use a Scroll compressor. Just make sure everything is clean and done to the best of your ability when you do the work. If you explain everything to the owner, then your conscience is clear, because it was his decision. Cheap people end up paying more in the long run by not doing the job right the first time.

    If he does ever call you for repairs, make sure you tell him labor isn't covered before you hang up the phone. Guys like that have a way of forgetting, and not wanting to pay. The contract will come in handy if he doesn't pay the service call and you have to go to small claims court.
    Why would you install a txv if it isn't needed?

    The real adverse issue here is why in the world would you put a new outdoor unit with an existing, unknown capatibility, indoor coil?
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  3. #16
    Join Date
    Jul 2005
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    5,293
    Quote Originally Posted by fliks View Post
    Could you explain why the orfice should possibly be slightly larger instead of smaller.
    The amount of liquid that flows through the piston depends upon the size of the piston and upon the pressure difference across it. Increasing either of these will increase flow.

    Since the 13 SEER condenser typically runs a much lower head presssure than the old condenser, you'd have to increase the piston size in order to get the same rate of refrigerant flow as before.

    Carrier allows matching 13 SEER condensers to preexisting piston metered coils. They provided dealers with a piston selection chart for that purpose.

    If you don't have something from the condenser manufucturer that tells you what size indoor piston to use, then a TXV is the best option. Also, depending upon the situation, it can be as cost effective or more cost effective to simply replace the coil. I won't say that coil replacement is absolutely necessary, because it isn't, unless your local or state codes require it.

    If replacing the piston is the only option given you, then the correct piston size can be found by trial and error. The correct piston is the one that provides the recommended subcooling for the condenser, and simultaneously provides a superheat value that corresponds to a standard superheat charging chart. Perfection isn't going to happen, it just needs to be in that ballpark as close as possible.

    Piston sizes marked on evaporator coil cases or in evaporator coil literature are immaterial, these are usually just telling you what piston the coil shipped with. But the piston must match the condenser, and should be resized accordingly for liquid line diameter, length, and rise. Indoor air volume should also be checked beforehand.

    A successful upgrade to a 13 SEER condenser on an old evap coil isn't out of the question, but it can take a bit of doing sometimes even when you know how to go about it.

    IMO, this should never be attempted on a heat pump system, straight cool only.
    Last edited by hvacrmedic; 02-11-2008 at 07:44 PM.

  4. #17
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  5. #18
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    Jan 2008
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    I'd be concerned about liquid reaching the compressor. Can the evaporator boil off all the excess refrigerant when you upsize the orfice? You might want to ask the apartmentment manager this question. I'm sure he'll know what you're talking about.

  6. #19
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    Quote Originally Posted by 2old2rock View Post
    I'd be concerned about liquid reaching the compressor. Can the evaporator boil off all the excess refrigerant when you upsize the orfice? You might want to ask the apartmentment manager this question. I'm sure he'll know what you're talking about.
    Piston metered systems are charged by superheat. The very purpose of superheat charging is to prevent flood back. Also FWIW, apartment managers in general aren't typically trained in hvac fundamentals.
    Last edited by hvacrmedic; 02-11-2008 at 07:43 PM.

  7. #20
    Join Date
    Dec 2007
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    89
    Find Another Co To Work For. Poor Customer Satisfaction!

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