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  1. #1
    Join Date
    Jul 2012
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    Jamaica Plain, MA
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    Insufficient cooling on 2 ton SEER11 central AC

    I have a 990 square foot condo with a 2 ton American Standard Allegiance 11 (Model: 2A7A1024A1000AA, manufactured 8/2004).

    I called a local HVAC contractor and he come out and diagnosed the problem as a "weak compressor." The compressor was under warranty so he ordered a new one. At that time he also replaced my capacitor as it appeared to have overheated (he showed it to me and it had a suspicious looking discolored spot at the base) and he cleaned the coils on the condenser.

    Today the tech returned to replace the compressor and filter and to charge me for his services. Now that he is finished....it is still not that cold in my apartment.

    I took some temperature readings with a digital kitchen thermometer just to get a handle on things...

    Indoor supply air temperature: 84.3
    Diffuser air temperature: 76.5
    Outdoor air temperature: 89
    Condenser output air temperature: 102
    Suction line surface temperature: 48
    Pressure line surface temperature: 92

    Should I get a second opinion? Should this problem be so hard to fix? Is there anything else I should check? What should I do next?

    As an additional note: The original compressor had a 10 year warranty, but the tech told me that the replacement part only has a one year warranty. Is this standard practice? Because it seems strange to me...
    Last edited by eherot; 07-12-2012 at 04:19 PM. Reason: Added additional note.

  2. #2
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    Jan 2009
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    Keokuk, IA
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    Interesting temperatures but they can't tell the whole story without pressures.

    I'm suprised you even need a 2 ton in a condo that small in that climate.

    Hoenstly, I wasn't aware that comrpessor got "weak". I genreally thought they ran until they locked out or went to ground.

    The 48F Vapor line temperature, but only 13F temp rise on the condensor makes me think charge is off, or restriction. If there's a restruction, then it might be overcharged nowand still have the restriction.

    Low indoor airlfow can't be ruled out either.

  3. #3
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    Jul 2012
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    Jamaica Plain, MA
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    Interesting temperatures but they can't tell the whole story without pressures.
    Would love to be able to measure this myself but of course that requires specialized equipment. ;-) I would have assumed the technician would have checked this before diagnosing the compressor problem, especially since I offered it to him as my "theory" about what was probably wrong with it over the phone.

    I'm suprised you even need a 2 ton in a condo that small in that climate.
    Really? I haven't had a detailed writeup done but basic guesses I was able to get from several web sites and charts made this seem like it was actually on the small size. At any rate the system was installed by the previous owner so I have no idea the logic that was used to size it.

    Low indoor airlfow can't be ruled out either.
    Might I be able to rule this out by measuring the output temperature at a point closer to the evaporator (e.g. by sticking a temperature probe directly into the duct just downstream of it)? As it is the diffuser where I measured that temp is probably only about 10 feet from the evaporator (~5' of which is flexible ducting). Other diffusers read a degree or two higher as I live in the third floor and the attic where the ducts are is typically about 125F. The flexible ducting is pretty well insulated but the main trunk has very thin insulation.

    The airflow seems very light to my untrained hand (it barely makes any perceivable noise at all when it's running) but I have little to compare it to. The same blower does not seem to have any trouble keeping the house warm in the winter, although I am on the third floor so presumably it doesn't have to work as well to get the job done.

  4. #4
    Join Date
    Aug 2007
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    Northern VA 38 degrees N by 76 degrees W
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    Quote Originally Posted by eherot View Post
    Would love to be able to measure this myself but of course that requires specialized equipment. ;-) I would have assumed the technician would have checked this before diagnosing the compressor problem, especially since I offered it to him as my "theory" about what was probably wrong with it over the phone.



    Really? I haven't had a detailed writeup done but basic guesses I was able to get from several web sites and charts made this seem like it was actually on the small size. At any rate the system was installed by the previous owner so I have no idea the logic that was used to size it.



    Might I be able to rule this out by measuring the output temperature at a point closer to the evaporator (e.g. by sticking a temperature probe directly into the duct just downstream of it)? As it is the diffuser where I measured that temp is probably only about 10 feet from the evaporator (~5' of which is flexible ducting). Other diffusers read a degree or two higher as I live in the third floor and the attic where the ducts are is typically about 125F. The flexible ducting is pretty well insulated but the main trunk has very thin insulation.

    The airflow seems very light to my untrained hand (it barely makes any perceivable noise at all when it's running) but I have little to compare it to. The same blower does not seem to have any trouble keeping the house warm in the winter, although I am on the third floor so presumably it doesn't have to work as well to get the job done.
    Did the service contractor not leave an invoice with pressures and temperatures? The other item that you can purchase and use daily would be a hygrometer for measuring the humidity in the space.

  5. #5
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    Jul 2002
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    Zelienople, Pa
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    Is the indoor coil a rated match to the ODU?
    How tall are you Private???!!!!

  6. #6
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    Furnaces often need a little less airflow than AC. You furnace might only need 600CFM while the AC needs 800CFM.

    THe hot attic is defnitely not helping. But off hand, it looks like you compressor is still...uhhh "weak". or more accurately it's not moving more than 1 ton right now.

    Tell them to come back and ask for the high side and low side pressure readings. IF possible the superheat and subcooling temepratures as well.

  7. #7
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    Jul 2012
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    Jamaica Plain, MA
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    Unfortunately the pressure readings were not written on the invoice. Only a basic description of the problem ("Compressor is weak, Pt. needs to be replaced"). If the tech wrote down pressure readings he did not give them to me. I will see if I can get him to send them to me or come back and re-measure.

    As for the coil rating and blower CFM/model number, that is going to require some serious crawling around in my attic so I'll have to come back with that tomorrow.

    Hydrometer would definitely be a worthwhile purchase though I think. I'll see if I can pick one up. Would be handy to have it anyway.

  8. #8
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    Quote Originally Posted by eherot View Post
    Unfortunately the pressure readings were not written on the invoice. Only a basic description of the problem ("Compressor is weak, Pt. needs to be replaced"). If the tech wrote down pressure readings he did not give them to me. I will see if I can get him to send them to me or come back and re-measure.

    As for the coil rating and blower CFM/model number, that is going to require some serious crawling around in my attic so I'll have to come back with that tomorrow.

    Hydrometer would definitely be a worthwhile purchase though I think. I'll see if I can pick one up. Would be handy to have it anyway.
    If the company that you used was not competent enough to write down on the invoice the measurements that where taken, if they where taken I would use a different company and specifically state that you want the airflow in cfm, pressures and temperatures for the refrigerant circuit, amperage and voltage of compressor, along with ambient temperature, and indoor supply and return. Without this information he would have only been guessing, and since the problem is still there, he more than likely was.

  9. #9
    Join Date
    Jul 2012
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    Jamaica Plain, MA
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    So I got some information from the unit in the attic in case this is of use here:

    Blower Model #: American Standard Freedom 80 Single-Stage (AUD060C924K4)
    Evaporator Coil Model #: Trane TXC024C4HPC0

    I wasn't really able to find much data on either of these, but judging by the model number alone it looks like the coil is a 24k BTU unit, which would make it the same as my condenser.

  10. #10
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    Jul 2012
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    Jamaica Plain, MA
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    So here's the response I received from the tech who worked on my AC after I asked him for technical details and measurements he took (copied verbatim, obviously):

    Hi Mr. Eric. The previous compressor was pump down. That means, the refrigerant was not traveling the way is support to be. After I changed it, high pressure was 220 psi low pressure was 75 psi. The pressures are reasonable, however still not enough gas arrives in evaporator. The nozzle in the evaporator may clogged. But the roof situation does not allow to service it. The panel for it is other side of the unit where the hundreds of nail is dangerously located. Thanks
    Mind you this is what he told me *after* I grilled him, not when he was accepting my payment and leaving my house.

    Some questions I have at this point:
    1. Is this something he should have been able to determine without replacing my compressor?
    2. What is the probability that *both* things were wrong with the same central AC?
    3. Does any of this seem weird or implausible to you? And,
    4. (Not sure if this is the right place to ask this but) do I have any recourse with this guy or am I just going to end up eating the $$$ cost to not fix my AC?
    Last edited by jpsmith1cm; 07-14-2012 at 06:36 PM. Reason: Pricing

  11. #11
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  12. #12
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    Doubt the compressor was the problem. If there is a restriction at the indoor metering device. That was probably the problem all along.

    Compressor was pump down? If that means it was going into a vacuum. Then that indicates that the compressor was working fine.
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    How many times must one fix something before it is fixed?

  13. #13
    Join Date
    Jun 2005
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    SW Wisconsin
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    Quote Originally Posted by eherot View Post
    I have a 990 square foot condo with a 2 ton American Standard Allegiance 11 (Model: 2A7A1024A1000AA, manufactured 8/2004).

    I called a local HVAC contractor and he come out and diagnosed the problem as a "weak compressor." The compressor was under warranty so he ordered a new one. At that time he also replaced my capacitor as it appeared to have overheated (he showed it to me and it had a suspicious looking discolored spot at the base) and he cleaned the coils on the condenser.

    Today the tech returned to replace the compressor and filter and to charge me for his services. Now that he is finished....it is still not that cold in my apartment.

    I took some temperature readings with a digital kitchen thermometer just to get a handle on things...

    Condenser output air temperature: 102F
    Outdoor air temperature: 89F
    The temp-split is only 13F, normally 107F or, an 18F temp-split

    Indoor supply air temperature: 84.3F
    Diffuser air temperature: 76.5F

    That is only a 7.8F temp-split; normally 16 to 20F temp-split.


    Suction line surface temperature: 48F

    Pressure-liquid-line surface temperature: 92F

    Condensing temperature 102F - 92F liquid line is 10F subcooling
    Using Approach Method 92F - 89F is 3F, usually 4F or above.


    Should I get a second opinion? YES
    Should this problem be so hard to fix? MAYBE
    Is there anything else I should check? YES!
    What should I do next? TAKE ALL THE TEMPS AGAIN & GET THE INDOOR HUMIDITY PERCENTAGE

    As an additional note: The original compressor had a 10 year warranty, but the tech told me that the replacement part only has a one year warranty. Is this standard practice? Because it seems strange to me...
    There is a very light load on the condenser therefore subcooling could look okay.

    That is why it is critically important to have adequate airflow through the indoor evaporator coil &, know that it is clean & absorbing close to its nominal Btuh Rating, which the condenser temp-split will indicate.
    Last edited by udarrell; 07-15-2012 at 10:54 AM. Reason: normally 107F ...

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