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  1. #1
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    Multiple Compressors over amping in refrigerated warehouse

    I’m having an issue with several 7.5 hp semi hermetic compressors over amping in a large freezer. I just started with my current company a year ago and have inherited this customer. Supposedly this issue has been happening at this site every summer. There are 5 systems all together in this box. Each with one evap and one compressor. So out of the 5 systems only 2 of them will fill the sight glass without over amping and shutting off on thermal. BTW these systems are OLD! I’m talking mid 80’s. One of the compressors still have a red Copeland plate.

    So last year when I took this site over and the ambient temps started hitting 80+, this started happening. Nobody warned me, but all the other techs new about it. The first think I asked, when were the condenser coils washed out. Of course, the reply I got was, ”Oh yeah, so and so did that like 2 weeks ago.” The coils didn’t look real dirty, so I had no reason to doubt it. At this time, at least 4 of the 5 compressors were over amping. It may have been all 5 I can’t remember. Someone even wrote all over these things to not charge to a full sightglass and to charge by amperage only.

    Before the end of last summer, one of these compressors give up the ghost. These were all originally 502 and sometime between 1985 and now, they got switched over to 408a. Don’t even ask! So, when I get the chance to change out this compressor, I switch it over to 404a. I also changed out the TXV along with filter driers and a new sight glass. I also blew out the system the best I could, but it has around 200ft of line set. About a month later I go back and change out the filter cores on the one I rebuilt and it has caught all kinds of thick tar like substance.

    As of right now, the only two that are running with a full sightglass is the one that I rebuilt and one other that had a compressor replaced about 6 years ago. One is on 404a and the other is on 408a so I know either refrigerant can work. I’ve replaced the filter driers on all the units and had to put new sight glasses on some of them. Friday I’m going out to wash the condenser coils and I wanted see if any one had some thoughts on what the issue could be. Right now, I’m leaning towards replacing TXVs and changing out the oil and filter driers again in all the systems that can’t take a full charge. I have a feeling these things are all gunked up with that tar crap and that’s why the sight glasses get so nasty inside them.

  2. #2
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    Start from the beginning.

    I agree the history is extremely important but if its not documented it doesnt exist.

    Clean all the condensers
    Clear the sight glasses
    Adjust SH at the pumps to 20 - 40*F

    Then start troubleshooting

  3. #3
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    Man it takes a lot of patience to work on some of those old dumpster fires...sometimes it's like, "Where do I even start?"

    I would just start with the most basic thing the customer will approve and go from there. For example, if the condensers are dirty I'd start with a real heavy duty cleaning.

    Sent from my SM-G960U using Tapatalk
    "Call a technician for God's sake. Or we'll see you on the news or the Dark Side of the Moon."

  4. #4
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    Is the power company providing consistent power during high usage summer months?
    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

  5. #5
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    How about Comp MN#s & SN#s and volt at the comp terminals and what volt is on nametag & what amp draw is allowed by the nameplate? What is suction & head press? What is ambient?

    By, red plate,you mean the nametag? If yes, then that simply shows how durable and well built a Cope Comp is!!!

    What is desired box temp & what is box temp?

    If you are looking for a Good Goffer, I'm available.OK a decent Goffer.

  6. #6
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    OP. OH I gotta ask, why "don't ask" about r408a?

  7. #7
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    Quote Originally Posted by TechmanTerry View Post
    OP. OH I gotta ask, why "don't ask" about r408a?
    Maybe he just doesn't like the color purple
    Officially, Down for the count

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  8. #8
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    Quote Originally Posted by 2sac View Post
    Maybe he just doesn't like the color purple
    I happen to think the new color is "cute", lol.

    As a matter of fact,I am trying to get a matching color for one of my Boxer Briefs.lol

  9. #9
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    Quote Originally Posted by TechmanTerry View Post
    I happen to think the new color is "cute", lol.
    I sold my first can of grey refrigerant yesterday. Happened to be 410a. Does anybody else see an issue with the new AHRI Guidelines? What could go wrong? We just had an issue where one of our distributors had sent us a pallet of orange 407c only it was orange 404a in 407c boxes...If they can't get colored cans in the right boxes....

    First we have gender neutral humans and now gender neutral refrigerant
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  10. #10
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    Thread Starter
    I actually like purple! This is my first experience working on equipment that’s been switched to 408a and I guess it just put a bad taste in my mouth. Also, I don’t know why someone would choose 408 over 404.

  11. #11
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    Quote Originally Posted by ImakesItCold View Post
    I actually like purple! This is my first experience working on equipment that’s been switched to 408a and I guess it just put a bad taste in my mouth. Also, I don’t know why someone would choose 408 over 404.
    Why not? I don't know myself. Just asking.

  12. #12
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    408a was/is a good refrigerant. It was the first replacement to 502 prior to 404a hitting the market. It's about 4 time the cost of 404a which makes 404a a no brainer.

    Your black sludge was from the POE oil flushing the remaining mineral oil and whatever other deposits in the system into the driers.
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  13. #13
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    Quote Originally Posted by ImakesItCold View Post
    I actually like purple! This is my first experience working on equipment thats been switched to 408a and I guess it just put a bad taste in my mouth. Also, I dont know why someone would choose 408 over 404.
    Back in the early to mid 1990's, R502's price started to increase dramatically making the new interim replacement refrigerants for R502 like R408A a more cost effective choice for retrofitting. Even as R404A became available and more common for new systems, R408A remained the go-to juice primarily because R404A would require a complete system oil change to POE and a TXV change.

    One particular characteristic of R408A is it tends to run hotter than R502, so it became more important to maintain a cold suction gas temperature to provide adequate compressor cooling.

    It was common back in the R502 days to have a suction/liquid heat exchanger installed in the system. They were used to help ensure a solid column of liquid at the TXV, but the side effect was they would also increase the suction gas temperature. As pecmsg stated earlier, the suction gas superheat at the compressor needs to be within 20-40F. To attain that, you first need to get your evaporator superheat running at about 6F. On those systems without a clear sightglass, it's unlikely those TXVs will ever feed enough to get that kind of superheat because their liquid supply will be flashing severely.

    So if your systems have heat exchangers, they should be removed. I suspect your "overamping" and internal overload trips may well be more a temperature issue than it is an amperage issue. A quick compressor performance check using Copeland's Mobile app or their online OPI page. Either will give you the expected amperage at any condition. You simply plug in the actual suction & discharge pressures and the measured amperage to have your answer. If your amperage is within 10% then you can eliminate the compressor as the problem.

    It would be helpful if you could provide compressor models as well as the condensing unit manufacturer and model.

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