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  1. #1
    Join Date
    Sep 2019
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    Low suction high liquid pressure

    So Iím a tech coming in after someoneís install. I was called out to look at a Lennox unit short cycling. Itís becoming the largest headache Iíve had to deal with in awhile at this point I have reclaimed and vacuumed down the whole system and added refrigerant but when the compressor kicks on the suction side drops quick and the liquid shoots up to well over 300 and then shuts off. I donít want to overcharge the system. But I canít figure out what the heck is the problem. Iím a bit newer only 7 years in and my master bailed before I got a full helpful training on ac. So if this is a stupid question I understand but Iíve never encountered this before. I need help.

  2. #2
    Join Date
    Jul 2011
    Location
    DFW, TX.
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    Dont take this the wrong way, but Bro...
    7 years? You got a restriction. How long have you been a tech?

    Sent from my LG-G710 using Tapatalk

  3. #3
    Join Date
    Oct 2011
    Location
    Chicagoland Area
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    Instead of giving you the answer, think about what is happening in the refrigeration cycle and what is supposed to happen. Start with what are the causes of low suction pressure.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  4. #4
    Join Date
    Sep 2019
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    2
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    Thread Starter
    I know, I know I only just started really doing service by myself for the last 2 years. Thank you, thank you.

  5. #5
    Join Date
    Jun 2017
    Location
    Phoenix, AZ (Previous: Texas, Oklahoma, Oregon)
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    52
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    Quote Originally Posted by Dadbod View Post
    I know, I know I only just started really doing service by myself for the last 2 years. Thank you, thank you.
    Are the service valves open? Lol

    Fixed orifice or TXV?

    Which way is your filter drier arrow pointing?

    I'd start with the basics

    Sent from my LM-G710VM using Tapatalk

  6. #6
    Join Date
    May 2016
    Location
    GA
    Posts
    139
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    Sounds like a restriction.
    Look at the TXV or piston which ever you have.
    Make sure service valve are open.
    Just slow down., think it out, and go through the refrigerant cycle checking every component that could restrict the flow.

  7. #7
    Join Date
    Aug 2018
    Location
    Piedmont Triad, NC
    Posts
    576
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    Nvm. Didnít read post properly. Sounds like a restriction like these guys said.

    At what pressure does it shut off? What is well over 300?

  8. #8
    Join Date
    Jul 2014
    Location
    Minnesota
    Posts
    304
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    Installers can be thoughtless at times. If you've tried to find it by temperature, put a piercing valve on the liquid line, if it's still 300psi check down stream what the installers have done. If it's low check what they did on the condenser side, then pump it down and fix the little hole.
    Installers rule of thumb, little solder good lots better. Little heat good lots better.

    Sent from my SM-S767VL using Tapatalk

  9. #9
    Join Date
    Jan 2010
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    300 / R410a ?

  10. #10
    Join Date
    Mar 2015
    Location
    Medford, N.Y.
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    5,864
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    You came along after someones install? So, I'm guessing r410a? What was room temp and ambient? What does "well over 300 psi" mean?

  11. Likes CEAS-AC-TECH liked this post
  12. #11
    Join Date
    Jan 2011
    Posts
    6
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    410a i am assuming you have a TXV.

    check for a temp drop across the liquid line filter/dryer also a temp drop from where the liquid line leave the condensing unit to where it enters the evap.
    check for a clogged screen at the txv if there is one there. also could just be a bad txv. like they said. just think about it without freaking out it will come to you.

  13. #12
    Join Date
    Oct 2018
    Posts
    39
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    300 psig for liquid line R 410A that's Not bad .. and how low is your suction line pressure ?? need Number .. you need to measure superheat and subcooling to make sure that there is a liquid line restriction .. if there is a liquid line restriction Evaporator coil will be starving for refrigerant and you're going to get high superheat on the other side refrigerant will be spending longer time in the condenser coil and releasing more heat and that leads to high subcooling too

  14. #13
    Join Date
    Oct 2016
    Location
    Clearwater, Florida
    Posts
    1,475
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    If you weighed in the charge and it's short cycling, most likely it's a restriction. Could be the drier, could be the TXV or piston or whatever you have.

    Sounds like a restriction though.

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