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  1. #1
    Join Date
    Feb 2008
    Location
    Florida
    Posts
    2

    6 Degree Delta T/Please Help!

    Hi I’m new in the business and trying to learn as much as I can and looking to get some help from you guys. I’m having a problem with my own A/C unit and can’t figure out what’s going on with it. Here is the situation:

    I’m getting a very low Delta T, around 6 degrees difference… 73 degree return air and 67 on supply. I put my gauges on and got 20 psig on the low side and 157 on the high side. The indoor temp was 75. The outdoor temp was about 80 to 85. The suction line temp at the condenser was 77. I checked the air filter, evaporator coil and condenser coil to make sure there was no blockage. I then felt the evaporator coil and found that it was cold only about 40%. It has a fixed metering device/cap tube. Being the rookie that I am, I decided that the evaporator was starved and to add some refrigerant (yes I do have my CFC) about 2 pounds. I fully expected the gauge pressures to rise and the suction line temperate to drop and I was ultimately hoping to get a 10 degree superheat based on my A/C charging calculator.

    After adding refrigerant the low side gauge rose to around 38 psig and the suction line temperature lowered only to 70 degrees. In my mind this equates to about 15 degrees saturation temperate and about 55 degree superheat. After realizing that adding refrigerant was not solving the problem, I put my tools away for the day and decided to think on it. Today I hooked up the gauges again and found that I’ve got 100 psig low side and 175 psig high side. The suction line temp was 70. I’m pretty confused about the change in pressure. I checked the evaporator coil and it’s still running only about 40% cool.

    I appreciate any feedback.

    Thanks,
    Last edited by DGALLE; 05-19-2008 at 06:05 AM.

  2. #2
    Join Date
    Jul 2001
    Location
    maryland
    Posts
    1,355
    I think you should put some more in it.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,879
    ID WB temp, OD DB temp, SH, and SC???
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Sep 2006
    Location
    Tampa Fl
    Posts
    105
    "I’m new the business"

    Sounds like India to me!!!

  5. #5
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    Sounds like DIY to me, or someone that can't read the rules.
    If everything was always done "by the book"....the book would never change.

  6. #6
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,317
    If you stop and think about "sequence of events", you can often answer your own questions (not always, but mostly). Review what you first found, what you did that you thought would change things, and then the end result.

    Your first assumption after your gauge and superheat readings was that the system was low on refrigerant. Adding refrigerant did not restore proper performance of the system. When you returned a day later, your readings were worse. What happened?

    First of all, unless you merely forgot to include such in your post, you did not measure subcooling, nor disclose what amperage the compressor was pulling under all three observation sets (when you first found it, after adding refrigerant, and the most recent gauge readings).

    Ask yourself what could cause a system to lose a significant pressure difference between suction and liquid sides, and you'll be on your way to solving the problem. Without that pressure difference, the refrigeration cycle effectively ceases to exist.

  7. #7
    Join Date
    Jul 2001
    Posts
    3,112
    Blower speed?

  8. #8
    Join Date
    Sep 2007
    Location
    Lufkin TX
    Posts
    72
    Are the valves leaking by?

  9. #9
    Join Date
    Feb 2005
    Location
    Miami, Fl.
    Posts
    3,559
    Not a DIY site....... Thread closed.

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