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  1. #14
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    Quote Originally Posted by sneuberg View Post
    While I don't know the exact figures, the preexisting system had enough air flow

    How many CFM per ton do you consider enough air flow?

    and the pressures/temperatures were reasonable.
    What are reasonable Pressure/temps, and at what outdoor temp they reasonable?

    The preexisting system had a SEER of at least 12.
    Don't hav a Preston book infront of me, but I thought your condenser maxed out at 11 SEER,

    The indoor unit was matched to the 3.5 ton outdoor unit. The new outdoor unit is a 3.5 ton unit and the installation manual says nothing about expecting a TXV.
    Just because they have the same nominal capacity rating, doesn't mean they will work right together.


    This probably deserves a new thread about mixing components from different manufactures and whether they can be matched. This thread asks the question: Can one detect if the cause of high head pressure is due to non-condensables in the sytem?
    While a test can be done. Your high head pressure won't be solved by it, your mismatch is what is causing your problem. See it a lot at apartment complexes.
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  2. #15
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    Quote Originally Posted by beenthere View Post
    While a test can be done. Your high head pressure won't be solved by it, your mismatch is what is causing your problem. See it a lot at apartment complexes.
    I've attached the White Paper that jimj mentioned (I assume this is the one).

    I would argue that the head pressure on these mismatched systems (13 SEER condenser/ 10 SEER evap coil) will run lower than it did with the old 10 SEER condenser, even with the original fixed metering device, but few would listen. Suffice it to say that Carrier found the SEER to run somewhere between 10 and 13 on the mismatched combinations that they tested. I don't see how that's possible when you're running a head pressure (per the OP) that corresponds more closely to that of a 7 or 8 SEER system.
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  3. #16
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    Quote Originally Posted by dandyme View Post
    I'm a little concerned with:
    "The more skilled technician found that the system was overcharged and reduced the charge as much as he could."
    I'm concerned about that as well. He can reduce an overcharge to a proper level, not just "as much as he could."

    I think if there is a better tech that the installer recommended, you ask the company service manager to send him out and see that the system is correctly charged. Tell him what you know, and let him evaluate the situation so he can make it right.
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  4. #17
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    Quote Originally Posted by hvacrmedic View Post
    I've attached the White Paper that jimj mentioned (I assume this is the one).

    I would argue that the head pressure on these mismatched systems (13 SEER condenser/ 10 SEER evap coil) will run lower than it did with the old 10 SEER condenser, even with the original fixed metering device, but few would listen. Suffice it to say that Carrier found the SEER to run somewhere between 10 and 13 on the mismatched combinations that they tested. I don't see how that's possible when you're running a head pressure (per the OP) that corresponds more closely to that of a 7 or 8 SEER system.
    They have another paper that shows the SEER at 8.something. And that to get close to 13 SEER, they system has to be over charged. But never reaches rated capacity of the condenser. Bristol compressor did a similar test, and came up with the same results, lowered capacity and lowered SEER.
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  5. #18
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    did they give you other options like replacing the indoor coil and outdoor unit with a 410a unit . did they check the indoor coil for cleanliness ,would think that a new evap coil that matches your outdoor unit will solve your problem

  6. #19
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    Quote Originally Posted by hvacrmedic View Post
    I've attached the White Paper that jimj mentioned (I assume this is the one).
    Yup, that's it thanks.
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  7. #20
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    Quote Originally Posted by sneuberg View Post
    The compressor in my Carrier model 38TRA042310 condenser failed after about 16 years of service. I guess that’s not unusual for Tucson, AZ.

    During the installation numerous errors were made; too numerous for this post, but the one that disturbs me the most is that they didn’t use a micron gage during the evacuation of the system. They relied on the manifold gauge which I later found out is old school. .
    16 years of service, and I bet my last dollar they did not use a micron gauge during the first installation 16 years ago. Your putting the cart way before the horse, your problem is most likely what others have mentioned, mix matched system, micron gauge will not fix that.
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  8. #21
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    Quote Originally Posted by beenthere View Post
    They have another paper that shows the SEER at 8.something. And that to get close to 13 SEER, they system has to be over charged. But never reaches rated capacity of the condenser. Bristol compressor did a similar test, and came up with the same results, lowered capacity and lowered SEER.
    I've attached that one below. A matched 13 SEER system wouldn't achieve 10 SEER either with the superheat running at 54.54°. IOW Bristol intentionally biased their results. With superheat adjusted to the target value the SEER will be over 10, which is how Copeland tested them.
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  9. #22
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    I think Bristol tested using factory charge, and adding charge to get capacity up. Which in order to cap up, the head then runs high.

    There is another one done by some one that got the same results as bristol.
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  10. #23
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    Quote Originally Posted by beenthere View Post
    I think Bristol tested using factory charge, and adding charge to get capacity up. Which in order to cap up, the head then runs high.

    There is another one done by some one that got the same results as bristol.
    I suggest that it was due to:

    http://en.wikipedia.org/wiki/Selection_bias

    My personal experience concurs with Copeland's study. We've installed a lot of these. If there had been issues, we wouldn't have continued. Install a TXV or the correct piston and in general the result is much better than 10 SEER.

    Absolutely no heat pumps though!

  11. #24
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    Quote Originally Posted by hvacrmedic View Post
    I suggest that it was due to:

    http://en.wikipedia.org/wiki/Selection_bias

    My personal experience concurs with Copeland's study. We've installed a lot of these. If there had been issues, we wouldn't have continued. Install a TXV or the correct piston and in general the result is much better than 10 SEER.

    Absolutely no heat pumps though!
    Oops! I meant to say Carrier instead of Copeland. Got some wires crossed. I'm not a big fan of Bristol, that could have been part of it.

  12. #25
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    Thanks for the information

    I’d like to thank all you for your input. Unfortunately none of them make me feel very good. The gist seems to be that I wasted a lot of money for a quick fix just so I could stay cool. I wasn’t expecting things to be perfect, but had I known that this fix was going to result in such high head pressures I might have declined. The tech that suggested this combination didn’t tell me that the results would be this bad.

    As a customer I don’t see how this could be my fault and I think I should receive some consideration. I’m just not sure what I can reasonable ask for.

    I’d still like to know what the procedure is to test for non-condensables in a system. I have no intention of trying to perform it myself, but I’d like to know. I find the HVAC field fascinating at least from a theoretical standpoint. I’ve started reading “Refrigeration & Air Conditioning Technology” by Whitman, Johnson Tomczyk and Silberstein. This textbook does state that non-condensables can cause high head pressure, but I can’t find a procedure to determine if that would be the cause.

    I know the gist of thread was that I should get off that horse and realize that my problem is a mismatched system. Still if you google the SEER rating of Carrier model 38TRA, Carrier sold it as having at least a SEER of 12 versus value of 10 that was discussed in this thread.

    If the procedure to check for non-condensables is easy, let me know what it is. I’ll have a tech from the company come out and check that, the air flow, the condition of the evaporator coil (not so long ago it was clean), the charge, and then I’ll know where I stand.

  13. #26
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    The fact that the old unit was a 12 SEER makes it even more unlikely that the high head pressure has anything to do with a mismatch. The most likely cause is a liquid line or metering device restriction.

    Noncondensables are another possibility. Was the nitrogen holding charged bled off at any time? Was the vacuum pulled on the entire system, or on just the line set and indoor coil?

    There are many ways to diagnose noncondensables. If your tech doesn't already know at least one of them, then have him recover the charge and replace it with new refrigerant. Or find one that does know how to test for them, or that can diagnose the real problem without wasting all that time and money.

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