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  1. #1
    Hi,
    I have been in automotive cooling repair for quite a while, but this house stuff seems a little different. I have a 3.5 ton unit at home that will not cool. I know that hvac units run higher pressures than automotive, but I keep getting different answers about what the pressures should be. My high side pressure seems low (225psi) and the low side is around 70psi. The high side line is nice and warm, while the low side is cool, not cold, or sweating. Does a system like this carry a txv or some kind of restricting orfice? I know it needs something to drop the pressure, but I have no idea where to look. I plan on getting a package system next spring and I would really like to make this system last a little while longer. Any help or advice would be appreciated.
    Thanks.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,179
    You need to come up with some kind of charging chart. There's some generic ones somewhere on here. Could be a fixed meter or a TXV though TXVs are normally found only on high SEER stuff. Don't go by suction line temp, newer units can run a slightly cool suction line and be right on.

    http://www.hvac-talk.com/fyi/Jim_Wheeler_Charging.pdf

    225/70 doesn't sound bad for an 80something afternoon but need to know much more. The chart above is pretty simple and ok for fixed meter if you don't have the mfrs. chart.

  3. #3
    Senior Tech Guest
    Could be fixed meter or expansion valve, go to "For your interest section" and read superheat and subcool section.

  4. #4
    check the airflow
    make sure the return filters and coils are clean.
    air flow is essential.

  5. #5
    Join Date
    Jul 2005
    Posts
    1
    It could be overfeeding if it's a TXV, which is unusally. Or the compressor isn't pumping right. If it's a heat pump the check valve at the evaporator could be leaking. But make sure its not overcharged and both coils are clean before you get carried away.

  6. #6
    The last two replies just blow my mind.

    There is not enough data to lead you guys to the recommendations that you have given out in this post.

    "check the airflow", just what leads you down this path?

    "70/225... over-feeding?????", yet you do not know whether this is a piston/txv system, AT, SH, SC, IDB, IWB, etc, etc...

    And I hope for our sakes you're not the ACMAN, I know from the past...

  7. #7
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
    Posts
    1,373
    Should call a pro HVAc tech ASAP, they are there for a reason. We don't want you to mess things up. Matter of fact they can show you how it's done.

  8. #8
    i chickened out and called a pro to look at this thing. I did everything right except give it enough freon, the 225/70 readings were at 95 degrees. Seems to be doing ok at the moment. The pro said that these 30 year old units hold more freon than the newer ones. I'll keep a eye on it and see how it does. I still plan on replacing the unit with a package unit.
    A room has been added and I need a 4 ton unit.
    Thanks for all the help.

    Starliner .( I'll stick to r-134 systems )

  9. #9
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    Package units are big, ugly things. You also can get more eff. units with a split system. Leave the package units for the mobile home customers.
    Karst means cave. So, I search for caves.

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