Results 1 to 12 of 12
  1. #1

    Angry

    i'm working with a matched 2 ton split air conditioning system. i went to pump down the refrigerant to perform a repair but each time the suction pressure will drop to about 20psi, stay there for a few seconds and then i'll hear a loud hissing sound and my suction pressures shoot up!. i had the discharge valve closed all the way. is the compressor bad??.. condenser ambient temp was about 80 degrees, inside kinda cool about 69 degrees. would slugging make it do that?... i appreciate any tips

  2. #2
    What type of repair are you trying to accomplish?

    Ever hear of a pressure relief valve?

  3. #3
    i'm gonna replace the air handler inside...no never heard of such a thing??..this is on a residential system

  4. #4
    Senior Tech Guest
    If you don't know what a pressure relief valve is one might tend to question your credentials....that is if you had any listed. Best tip I could render to you at present, not knowing your experience, would be to call a professional.

  5. #5
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The system has more refrigerant in it than can be stored in the condensor coils.

    As the condensor fills up with liquid, there is less coil volume available for condensing refrigerant into a liquid, and the discharge pressure goes up. When the condensor coils get about 80% filled with liquid, the pressure will REALLY spike up and the compressors internal pressure relief will open to relieve pressure into the case of the compressor, causing your low side pressure to go up.

    You will be able to pump the system down if you remove some of the refrigerant from the system first.
    If more government is the answer, then it's a really stupid question.

  6. #6
    overcharged, to much refrigerant in system and condenser cannot handle it and compressor internal bypass opening.

  7. #7
    ok what you guys are saying makes sense to me, thanks for the help. i don't really have that many credentials to be honest with everybody here, but i don't think any of you guys did either when you first started out in the trade. i just turned 18 a month ago and i've been learning this stuff since i started working for this maintenance company when i was 17. i'm very interested in this trade and would love to persue a career in it. i think i know a lot for my age right now as i'm just entering the field.

  8. #8
    something that i did notice though that makes sense from what you are saying is the excessive lenth of the freon lines. i think that combined with the fact that the condensing unit is small is the cause of my problem. the lines are at least 100 feet long on each side if not longer. this is on an apartment which is located right in front of the laundry room, the lines go all the way to the other side of the laundry room and then about 30 feet more.
    i will try that out though and recover some of the refrigerant and pump down the rest. i hate my slow recovery machine which only recovers vapor for me.

  9. #9
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,956
    Learn the fundamentals concerning sizing, duct systems, and airflow. Learn to apply manuals, J, D, and S.

    If the systems you evaluate pass those standards, then you can check the charge using both Superheat and Sub-cooling.

    http://www.udarrell.com/ac-trouble-s...ubcooling.html

    http://www.udarrell.com/ac-trouble-shooting-chart.html

    Always check the temp split off the condenser and keep records of all the units and their particular condenser's CFM.
    This procedure can be used to check the gross and net Btu/hr heat ejection from the conditioned space.

    There is a lot to learn however in checking performance and trouble shooting; --following the proper procedural sequence is a first order essential to your effective performance as a tech. - Darrell



  10. #10
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,956
    Learn the fundamentals concerning sizing, duct systems, and airflow. Learn to apply manuals, J, D, and S.

    If the systems you evaluate pass those standards, then you can check the charge using both Superheat and Sub-cooling.

    http://www.udarrell.com/ac-trouble-s...ubcooling.html

    http://www.udarrell.com/ac-trouble-shooting-chart.html

    Always check the temp split off the condenser and keep records of all the units and their particular condenser's CFM.

    This procedure can be used to check the gross and net Btu/hr heat ejection; which may or may not be from the conditioned space. (I.E., hot attic air, etc., leaking into the Return Air ducting; compare condenser split with evaporator split temps.)

    There is a lot to learn, however, in checking performance and when trouble shooting; --following the proper procedural sequence is a first order essential to your effective performance as a tech. - Darrell

  11. #11
    Join Date
    Jul 2001
    Posts
    3,112
    You can't store all of the charge in the compressor. It won't hold it. You can't close the discharge valve and n run the compressor.

  12. #12
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,956
    Originally posted by troyorr
    You can't store all of the charge in the compressor. It won't hold it. You can't close the discharge valve and run the compressor.
    I would hope he meant that he shut off the condenser service port valve! The compressor does not store refrigerant, it pumps hot gas through the discharge line to the condenser.

    Most residential condensers' don't have a discharge line shut-off valve. It could be handy for sealing off the refrigerant charge in the condenser when replacing a "mechanical failed" compressor. Darrell

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