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  1. #40
    Join Date
    Jul 2006
    Location
    West Plains, Missouri, United States
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    85
    Quote Originally Posted by INTECHBILL View Post
    This happens whenever the compressor absorbs heat instead of rejecting it ! Many causes ! Read the book ..
    The compressor creates heat. It does not absorb heat! Not unless the entering gas temperature from the suction line is hotter than the compressor.
    The refrigerant gas returning to the compressor either absorbs the heat produced by the compressor, or it will be to super-heated to absorb that heat, thus not helping cool the compressor. In short, the refrigerant removes the heat created in the compressor, (ie: Heat of compression), or the compressor will most likely overheat. (Assuming it does not have some other external means of cooling the compressor).

  2. #41
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,035

    Frown Lack of airflow destroys compressors

    mcewans:
    -------------
    Stuart
    Lack of airflow destroys compressors.
    Amen to that!

  3. #42
    Join Date
    Jul 2006
    Location
    West Plains, Missouri, United States
    Posts
    85
    Quote Originally Posted by frozensolid View Post
    I have to disagree with that. If you are dealing with a properly charged system lets say its 12 degrees subcooled. When you disconnect the fan subcooling will increase very rapidly. The sudden increase in pressure would increase the condensing press/temp right away but it would take time for the liquid to catch up so to speak.
    This would result in a net increase in sub-cooling.

    If all that liquid flashed to gas instantly and superheated I would expect catastrophic condenser failure from the pressure rise.

    Maybe I am not just thinking right so please correct me if I am wrong.
    Assuming you do not reach the "Critical Temperature" of the refrigerant first.

  4. #43
    Join Date
    Jul 2006
    Location
    West Plains, Missouri, United States
    Posts
    85
    The temperature corresponding to your gauge pressure, should be higher than that indicated by the thermometer on the suction line in order to have sub-cooling.
    If the sub-cooling is indicating a negative sub-cool. Then that sounds like your line temperature is above the temperature indicated by your gauges.

    I am guessing it has an undercharge. The refrigerant should be in a liquid state well before leaving the condenser. I am guessing it is not. It is still a supper-heated gas, or liguid gas mixture.
    Or as the others stated, lack of air flow.

  5. #44
    Join Date
    Dec 2010
    Location
    Waco, Kentucky
    Posts
    66
    I was on a new install a few days back. Complaint was the it was not cooling well. Residential 2 ton condenser, 2.5 ton coil and 70k BTU 80% GF with a 3 ton drive. Not positive it was 70k Btu but defiantly a 3 ton drive. It had a clean filter, clean coils, the correct piston and fan speed matched accordingly to the 2 ton condenser. I didn't check wet bulb but I know the dry bulb return at the coil was 78 and supply 63 with a SH or around 15. It was 98 outside and the condenser was in direct sunlight. My concern was that I had no SC. Actually the liquid line had 3 deg SH. I've seen this same issue with several units lately. So my questions are this: What could be the problem? and How do I fix it?

  6. #45
    Join Date
    Jul 2006
    Location
    West Plains, Missouri, United States
    Posts
    85
    Quote Originally Posted by john_dixon29 View Post
    I was on a new install a few days back. Complaint was the it was not cooling well. Residential 2 ton condenser, 2.5 ton coil and 70k BTU 80% GF with a 3 ton drive. Not positive it was 70k Btu but defiantly a 3 ton drive. It had a clean filter, clean coils, the correct piston and fan speed matched accordingly to the 2 ton condenser. I didn't check wet bulb but I know the dry bulb return at the coil was 78 and supply 63 with a SH or around 15. It was 98 outside and the condenser was in direct sunlight. My concern was that I had no SC. Actually the liquid line had 3 deg SH. I've seen this same issue with several units lately. So my questions are this: What could be the problem? and How do I fix it?
    As per the AOP Rules only Professional Members * can reply with advice to the OP. Anyone may post and ask questions. They may even question the * member answer but not give advice or expand on the advice given. Please read these rules for a complete understanding. AOP Rules

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    Last edited by beenthere; 07-24-2011 at 09:58 AM. Reason: No *

  7. #46
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,035

    Lightbulb

    Quote Originally Posted by john_dixon29 View Post
    I was on a new install a few days back. Complaint was the it was not cooling well. Residential 2 ton condenser, 2.5 ton coil and 70k BTU 80% GF with a 3 ton drive. Not positive it was 70k Btu but defiantly a 3 ton drive.

    It had a clean filter, clean coils, the correct piston and fan speed matched accordingly to the 2 ton condenser. I didn't check wet bulb but I know the dry bulb return at the coil was 78 and supply 63 with a SH or around 15.

    It was 98 outside and the condenser was in direct sunlight. My concern was that I had no SC. Actually the liquid line had 3 deg SH. I've seen this same issue with several units lately. So my questions are this: What could be the problem? and How do I fix it?
    First, we need an accurate Return Air Wet bulb temp, or; %RH we can convert to WB; so we can see if the Superheat is high or on target.

    We also could use an amp-draw number; that has to be compared to the average readings U got with similar conditions. At 78F RA a WB of near 70F could result in total amps 'around' 9.9-amps.

    The lack of Subcooling could indicate an under charge. If the latent load is normal or low that could point to a low charge.

    At an outdoor 98F & mid-range indoor humidity the superheat target is 5F; U had 15F, too high - low charge.

    Is that a single speed condenser fan motor?
    Is the fan motor delivering the Rated condenser CFM?

    Check the condenser discharge air temp-rise. What was the head pressure?

    We need to determine the level of the BTUH load on the condenser; we need to know if there is an excessive evaporator heatload. Or, could something be starving the evaporator coil?
    Last edited by udarrell; 07-24-2011 at 10:20 AM. Reason: Is something starving evap...?

  8. #47
    Join Date
    Dec 2010
    Location
    Waco, Kentucky
    Posts
    66
    udarrell: I only have two years in the trade and I am still acquiring the necessary tools. Psychrometer is still on my to purchase list. A brand suggestion would be helpful. I have considered the undercharged idea but i have to get my SH down so low that I'm afraid it may bring back liquid under a lesser load. Yes it is a single speed cond. fan mtr. I did not check if it was delivering the rated CFM or temp rise. Head was 100 deg sat so around 325 psi. By starving do you mean refrigerant or air flow? Is there a chart or calculation available that includes all important measurements and information that will result in the precise SH and SC measurement for the given situation? Every time I talk with an experienced tech I get to relearn how little I know and how much more I have left to learn about this trade. Thanks for all the help.

  9. #48
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,803
    Every time I talk with an experienced tech I get to relearn how little I know and how much more I have left to learn about this trade.
    You have no idea how much more you have left to learn. And i have no idea how much more I have to learn either. Our trade is constantly changing, so learning is a never ending process.


    As soon as you get your post count to 15, apply for pro membership. So you have access to the pro forums, where we can go into detail, and help you learn. Can 't go into too much in the open forums. And this thread is about at the limit of what can be said.
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