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  1. #1
    Join Date
    Nov 2011
    Posts
    15

    Overcharge or undercharge 410A system

    Yes I could use some help and yes I have the universal esco certification to handle refrigerants.

    My problem is that I am new to the trade after finishing trade school and I am attempting to recharge my home 410A system.

    I will post the stats on my American Standard 4 ton fixed orifice system.

    By fixed orifice I understand that super cool is the most accurate way to charge the system.

    The unit is presently cooling within the following parameters. If I am in the wrong place to post this or no one can help fix this I understand.

    Line set = 40 feet (kind of a long one after we moved the condenser to the other side of the house.

    Ambient for afternoon: 83 F

    Head pressure: 118F 83 + 35 = 118F more or less shows on the high side gauge if I understand this correctly.

    Low side pressure: 125 psi = 42 saturation temp. 66.2 low side line temp.
    High side pressure: 335psi = 104 saturation temp. 83.1 high side line temp.

    Temp at the vent in rooms: 56.1F + or minus
    Temp from supply side: 55.2F
    Temp for return side: 68F

    When I figure super heat or sub cool on these saturation temps and line temps my super cool/sub cool show I guess a major overcharge. The outside low side line is just sweating a little not much and not icing up.
    66.2 – 42 = 24 superheat
    104 – 83 = 21 sub cool

    I have added virgin 410A to the system but I can’t believe it needs more added unless the long line set to the A-coil needs more to charge it properly above the 4lbs. 56 ounces stamped on the unit.

    Does anyone have any ideas I can try to tune this unit “right” on for the summer?

    Any advice would be appreciated.

    Thanks in advance.
    wlamore

  2. #2
    Join Date
    Dec 2011
    Location
    San Antonio, TX
    Posts
    381
    Charge according to Superheat...you need to know indoor ambient and return wet bulb along with odt next time you check.

    Sent from my ADR6350 using Tapatalk 2

  3. #3
    Join Date
    Feb 2012
    Posts
    1,268
    Fixed orifice charge is checked with superheat, the high superheat indicates a low charge or restriction.

    The factory charge that you see stamped on the unit only covers up to 15' of lineset, and I believe you have to add 3oz of refrigerant for every 5' of lineset past 15'.

    If you have the tools I would weigh out the refrigerant, and weigh it back in with the additional charge required.

  4. #4
    Join Date
    Aug 2002
    Location
    Sacramento area
    Posts
    69

    Question ???

    Quote Originally Posted by wlamore View Post

    Ambient for afternoon: 83 F ...

    Head pressure: 118F 83 + 35 = 118F more or less shows on the high side gauge if I understand this correctly. ...

    High side pressure: 335psi = 104 saturation temp. 83.1 high side line temp. ...

    104 – 83 = 21 sub cool ...

    the 4lbs. 56 ounces stamped on the unit.

    wlamore
    I'm not sure what you mean by the phrase "Head pressure: 118F 83 + 35 = 118F"

    Head pressure and High Side Pressure are the same, and pressure is in psig, not degrees F.

    You indicate the liquid line is 83F and the ambient air that cools the high side refrigerant is also 83F. It's not possible for the air to cool the refrigerant to the air temp of 83. Are you sure the liquid refrigerant temp sensor is actually reading liquid line temp or is the sensor uninsulated and reading ambient air temp, thus giving you false subcooling information?

    The unit data tag will not read "4lbs. 56 ounces", so maybe you have a typo or wrong information.
    I'm still learning this trade.

  5. #5
    Join Date
    Jun 2006
    Posts
    2,265
    High Superheat with High Subcooling.

    Liquid restriction or improper refrigerant metering causing liquid refrigerant to stack in condenser (High Subcooling) and not meter back to compressor (High Superheat)

  6. #6
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    If you have a matched coil on a 40' lineset I'd say you are about 15 oz undercharged. 40-15'=25' 25x.6oz per ft. = 15 oz. Being nearly a pound shy on a system this small is surely not going to work very well. Weigh in the extra 15 oz and check your readings again.

    hey wait a minute what's with this "I have added virgin 410A to the system but I can’t believe it needs more added unless the long line set to the A-coil needs more to charge it properly above the 4lbs. 56 ounces stamped on the unit." You have a 4 ton condensor that only holds 4lbs of refer? I don't think that's right. Most of the american standards I work on have between 10 and 13 lbs of r410a in them. check that label again...
    Last edited by Black Adder; 05-27-2012 at 01:36 AM. Reason: mistake reading op
    "Go big or Go Home"

  7. #7
    Join Date
    Dec 2011
    Location
    somewhere between here and there
    Posts
    478
    i dont suggest charging by super cooling.......you will get burnt evertime the muffler bearings are engaged.


    Please, Please Please......keep the Factory Smoke in the Wires!!!!!


    Is it Rum'Oclock yet???

  8. #8
    Join Date
    Dec 2011
    Location
    somewhere between here and there
    Posts
    478
    and the rating plate says 4lbs. 56 oz.....that is the amount of charge you should add if the super cooling is out of whack.
    Last edited by BigBacardi; 05-27-2012 at 02:10 PM. Reason: typo


    Please, Please Please......keep the Factory Smoke in the Wires!!!!!


    Is it Rum'Oclock yet???

  9. #9
    Join Date
    Nov 2011
    Posts
    15

    New informaiton

    sorry I got a few things wrong.

    1. I was told that head pressure could be estimated with adding 35degrees to the ambient and that should be close to the actual head pressure. However if it is the psi showing on the high side gauge is the head pressure why estimate it at all?

    2. The unit is an American Standard 14-seer, 2.5 ton AC with a 3 ton coil. It appears to be a fixed orifice looking at it attached to the coil. It for sure is not a TXV.

    3. It is stamped 4lbs 15oz. for the manufactures charge of 410A

    4. Last check by the tech from the company that installed it before going out of warranty was High side 275 psi, high side temp 70F, Low side psi was 115 Low side temp 50. This calculates to Super Heat of 12 more or less.
    He neither added or subtracted any 410A at that time. Was working fine.

    Can't think of anything else

    Thanks

  10. #10
    Join Date
    Oct 2010
    Location
    Baton Rouge, LA
    Posts
    1,113
    Get the installation owners operating manual for your unit. It should have a charging chart along with the information for long-line application.

    Superheat averages are used when checking a system that does not have a charging chart available, but many OEM's provide a chart with significantly different numbers. For instance, some Carrier condenser provide a chart to use based off the LLT and the LLP within a range of ambient temp. Another Carrier wanted a SH of 5° delta.

    Get the information from the OEM.

    On the other hand, Why were you charging the unit to begin with? Did you have a problem? Was something not working?

    I think you are looking for zebra's. Looking for Zebra's is a common medical term used to explain the action of people new to an industry searching for problems or rare complicated problems when one doesn't exist.

    The term comes from the phrase, "If you hear hoof beats look for the horse not a zebra." A zebra is nothing more then a horse with fur colored in strips. Just because you hear hoof beats don't expect to see a rare zebra.

    Another problem new technicians run into is called self-fulfilling prophesy. This means you think something is going to happen and inadvertently make all the evidence appear to fit you self prophesied results. ie: This is gonna be a low charge issue I know it. Yup my superheat is high its low charge. High superheat alone does not mean you have a low charge but your self fulfilling a predetermined problem.

    These issues usually go away as you become more knowledgeable in the field. Just take your time and tamper down yourself. Chances are you are not gonna find a rare strange problem your first year in the field. HVAC has been around for many years most issues have been addressed many times many years ago.
    If you're too "open" minded, your brains will fall out.
    Artificial intelligence is no match for natural stupidity.

  11. #11
    Join Date
    May 2011
    Location
    Oklahoma
    Posts
    362
    I think you've got your head pressure/ambient temp thing a little confused. Its not to estimate the pressure. Some people charge systems by taking their high side saturation temp various amounts above ambient conditions. Personally I've seen systems grossly overcharged using this method alone.

  12. #12
    Join Date
    Aug 2010
    Posts
    2,613
    I'd like to see a picture of this tag. 4 lbs 56oz?
    Why can't they just write 7 lbs 8 oz or 120oz?

  13. #13
    Join Date
    Nov 2011
    Posts
    15
    Look above, I posted I made a mistake, it is 4lbs. 15 oz.

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