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  1. #1
    Join Date
    Jun 2011
    Location
    MN
    Posts
    26

    Questions I am afraid to ask my boss and co-workers

    #1 Is RLA and FLA the same thing?

    #2 How close to RLA or FLA should a compressor be?

    #3 Should I hook my high side gauge up to the discharge service valve or the king valve on the receiver? Does it matter?

    #4 If I service a newer small refrigeration system (which is mostly what I do) and I put in a liquid line filter drier when it didn't have one before...how do I adjust the charge?

    #5 Got into a little argument with a co-worker who has more experience than I do...Me less than a year...him 3 years. I consider us both good techs who want to be as good as we can be and we both actually care about doing things right. Neither of us claim to know everything. It's an air conditioner in the local sugar plant. It cools a room full of electric equipment. The condensing unit is out in the hallway where it is always 80 to 90 degrees. 5 ton unit, no receiver. The evap in the electric room is a walk in cooler type evap with a TEV...I don't have model or make or size...The boss said put it in and I put it in and I have to assume he sized it correctly. I installed a sight glass on the liquid line a few inches from the condensing unit. It always bubbles. We were doing maintenance at the sugar plant and my buddy was concerned about the sight glass bubbling. I hooked up gauges 225 PSIG head=110 degrees. 15 degrees subcooling. Suction was 75 PSIG=44 degrees. Superheat was 17. My buddy wanted to add gas til the glass cleared. I said it was charged okay based on the subcooling. He wanted to know why it was bubbling if the charge was okay. I said I didn't know but i didn't think it needed more gas. Who is right who is wrong and why?

  2. #2
    Join Date
    Jul 2011
    Location
    Lehigh Valley, PA
    Posts
    427
    I think your head pressure is a little low. I'd look for about 250psi.

    I would use the discharge service port to read high side. Many small units only have a king valve so this would need be used in the absence of a discharge port. You would charge at the king valve after evacuation. Full load amps, running load amps. Same thing, right?

  3. #3
    Join Date
    Jun 2011
    Location
    MN
    Posts
    26
    Cpaz said: Full load amps, running load amps. Same thing, right?

    I think so. I guess that is why I asked. I'm not sure.

  4. #4
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,011
    Don't ever listen to anyone who says "I usually charge to x pressure "

    If you can get used to looking at sat temp instead of pressure you will be on the right track. Because pressure is relative to the design unit you are working on.

    I would tend to think you had measurement error with 15 deg sc and bubbles.

    Yes rla and Fla are same thing and anytime its close I'm looking into why. Usually a 208/240 unit will show Fla at 208.

    As far as high side guage connection if you were measuring the hot gas line you will not be accounting for pressure drop through condenser coil. The pressure at the reciever will be slightly less. This may lead to innacurate subcooling calculation. Maybe why you thought you had 15deg.

    Go to efficientcomfort.net and check out waynes brain analyzer. Learned a ton from that very useful tool.

  5. #5
    Join Date
    Oct 2010
    Location
    AZ
    Posts
    641
    Quote Originally Posted by SBKold View Post
    Go to efficientcomfort.net and check out waynes brain analyzer. Learned a ton from that very useful tool.
    Hey, thanks for that link. Looks like some useful stuff on there.

  6. #6
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    537
    Quote Originally Posted by cswenson218 View Post
    Cpaz said: Full load amps, running load amps. Same thing, right?

    I think so. I guess that is why I asked. I'm not sure.
    RLA is used when referring to motors in a hermetically sealed environment (refrigerant cooled windings). FLA is used with any motors that use ambient air to cool the windings. At least in Ontario, the rules for sizing OL and over current protection are different if the equipment has a RLA rating compared to a FLA rating. You can check your local electrician code for details

  7. #7
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,911
    Quote Originally Posted by LKJoel View Post
    RLA is used when referring to motors in a hermetically sealed environment (refrigerant cooled windings). FLA is used with any motors that use ambient air to cool the windings. At least in Ontario, the rules for sizing OL and over current protection are different if the equipment has a RLA rating compared to a FLA rating. You can check your local electrician code for details
    In the US (Canada studiously avoids choosing to do things the same way as the US, for nationalist reasons) the FLA "nameplate" rating of a motor is used to choose the overload protection used for the motor.

    The US-based National Electrical Code uses table values in Article 230 to determine conductor sizing for the motor. You look up the motor by HP, voltage, and phase configuration, and use the table current value x 1.25 to choose the appropriate conductor size using the conductor ampacity tables.

    Here is a previous thread on the use of these RLA and FLA acronyms:

    http://hvac-talk.com/vbb/showthread....RLA-verses-FLA

    In the case of motor-compressors, Article 440 covers the installation of condensing units.
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  8. #8
    Join Date
    Aug 2012
    Posts
    2,594
    Great thread, I would worry about a boss that I can't ask questions to. Those type are always tough to work for.
    My name is TooCoolforschool and I am a chronic over charger.

  9. #9
    Join Date
    May 2010
    Location
    Oxford, UK
    Posts
    336
    We look after some R22 milk coolers that don't have recievers, just automotive style reciever/driers which have a built in sight glass. We charge them till the sight glass just clears (R404A may have few bubbles in even though charged ok). Pumping the system down will show if its been seriously overcharged as it will trip on hp before suction is at 0psi. If it was a walk in cooler would check the suction superheat at the evaporator outlet somewhere between 9 and 13 is typical depending on load rooom temp and sizing.

    I'd probably have weighed some refrigerant in to see how it ran, but would be ready to get the recovery machine out to remove it again if it wasn't happy!

  10. #10
    Join Date
    Dec 2009
    Posts
    147
    Never ever be concerned with asking a stupid question. You are an apprentice .... and anyone who chastises you for a dumb question isnt worth working for.
    Welcome to the trade!!

  11. #11
    Join Date
    Jun 2011
    Location
    MN
    Posts
    26
    I think I misspoke and unfairly painted my boss as a jerk...I should have said I am too embarrassed to ask some questions. I usually try to find my own answers either here or from a book. I'm a new guy, but I'm older and get self conscious when I don't know something or can't find the answer or figure it out on my own.

    That being said...how I usually charge a system. I don't go by pressure. I try to think temperature. I weigh in the charge when I know that information. Then I look at condenser split and TD. Then I make sure there is some subcooling if it has a receiver and a TEV and I make sure the superheat is okay. I heat the receiver and make sure it is a quarter to a half full unless it has head pressure control, then I like to go a little more. If everything is reasonable and the glass is still bubbling I call someone and ask what the hell I should do now.

  12. #12
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Since the RLA/FLA thing has been cleared up ill weigh in on the charge thing. If it has a sight glass and a TEV and bubbles its wrong. The TEV must have a full column of liquid to do its job correctly. If it does not it will hunt continuously. Some subcooling does not = a full charge. With a TEV a full column of liquid feeding that TEV under all ambient conditions= full charge. On the system you have I'd say fill the glass first then take readings. Cannot adjust TEV to set superheat without full column of liquid. Gotta be checking liquid pressure to know what your subcooling is. You can check discharge super heat with discharge pressure.

  13. #13
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,594
    Have any of you guys ever seen a full sight glasses with 10 degrees subcooling?

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