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Chiller troubleshooting

Discussion in 'HVAC' started by Pascal, Jul 29, 2021.

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  1. Pascal

    Pascal Senior Member

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    Follow up on my breaker curve thread

    https://www.yachtforums.com/threads/schneider-breakers-curve-type.35015/

    it wasn’t the breaker... I replaced it and it still trips. Need to come up with a good troubleshooting strategy.

    system has three dometic chillers but for some odd reason the dometic 22D3466C-4DE0-4FBA-AEFF-DC6022864380.jpeg A434224F-E5AB-4BA4-8B32-6B6DB97D2160.jpeg control box only has two inputs from the main electrical panels. 1 input for chillers 1 and 2, second input for chiller 3 and the two pumps. As per the diagram in the cruisair box, each chiller should pulls 23 amps and each pump about 8amps. So each input is well within the main panel 63 amp breakers capacity. The chillers use freq drives so no start up load

    Problem is that when both chiller 1 and 2 are running, the 63 amp breaker on the main panel trips sometimes after 30 minutes... sometimes after 8 hours.

    started happening about 2 weeks ago

    if I disable either of them, it doesn’t trip but while two chillers do the job after 7Pm... by 10 am I need all three

    trying to come up with a troubleshooting strategy... I m thinking of using the Max function on a Fluke clamp on meter to see if I can see a spike.

    each chiller is protected by a 40 amp Breaker inside the cruisair box so in theory I could increase the amperage of the main panel breaker but I just don’t like the idea

    any suggestion?
    Last edited: Jul 29, 2021
  2. mapism

    mapism Senior Member

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    Ideally, it would be nice to have two clamp on meters, and leave one on them on each line (#1 and #2), checking the respective peaks the next time the 63A breaker will trip.

    Alternatively, you could replace the 40A breakers with 30A ones, and see if it's always the same chiller that trips its own breaker.
    In fact, with 2x30A breakers, either one or the other must trip before the common 63A does.
    That should at least identify the culprit.

    That aside, how many running hours did each chiller clock so far? Those things don't last forever...
  3. Pascal

    Pascal Senior Member

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    B13CC418-8C8F-4BE7-865F-DF628BC19BDB.jpeg They were replaced 3 years ago so when is no issue. Recently cleaned and when running they re only pulling about 42 amps combined which is less than the 46 the dometic data shows and far less than the 63 amp breaker capacity.

    Replacing the individual 40 amp breakers with 30 amps is a pretty good idea, I may try that next of the clamp on meter doesn’t yield any clue.

    If anything since I replaced the 63amp breaker, the problem has gotten worst, tripping after as little has 30 to 60 minutes.

    this is the graph on my phone get from the monitoring sensor on the loop. On the left, yesterday afternoon you can see the peaks when the breaker had tripped and then quick drop as soon as it was reset. Around 8Pm, I shut down chiller nr 1 so loop temp came back down slowly. Starting around 10 am, 2 chillers were not enough and temp started rising. At 15:31 I restarted chiller nr 1 and you can see the quick drop.

    then the up and down ecah time the breaker tripped and was reset
  4. mapism

    mapism Senior Member

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    Mmm... A puzzling situation indeed. No other ideas at the moment, I'm afraid.
    But I'll follow this thread with interest, because I'm curious to hear about your findings.
    Good luck!
  5. Capt J

    Capt J Senior Member

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    Usually dirty chillers draw more amps. You need to turn off one of the 40 amp breakers and monitor load, one at a time. If you change the 40 amp breakers to 30's they will trip......probably right after startup. if it goes 30-60 minutes, it sounds like you have a loose connection or possibly bad wire on one of the lines going to a chiller, or compressor is starting to go bad on one.......
  6. Pascal

    Pascal Senior Member

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    Descaled a month ago, coil temperatures are fine and even. They re on freq drives so no startup surge.

    Been monitoring start up and run amps for either chillers and combined. Well within specs.

    When running one at a time, no tripping.
  7. mapism

    mapism Senior Member

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    Why? The rated absorption is 23A each, and Pascal said that usually they are actually pulling 42A combined, which means 21A each on average. How likely is it that both exceed 30A simultaneously?
    My guess is that only one of them has a freak behaviour, hence my 30A breakers idea to identify which one.
    Nothing to lose with this test, anyway!
  8. Capt J

    Capt J Senior Member

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    I agree that it sounds like 1 compressor is going bad. But can also be a loose connection on a chiller too, that will make it draw more amps once in a while.
  9. mapism

    mapism Senior Member

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    Yup, that's another possibility, also because usually compressors vibrate a bit, particularly while cycling on/off.
    I'd be surprised if Pascal didn't already check the wires connections at the breakers end, but maybe he didn't on the chiller side?
  10. Pascal

    Pascal Senior Member

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    Indeed I check all the visible wiring, nothing obvious including in the chiller control cabinet. That’s why I need to narrow it down to one chiller.
  11. johnnry

    johnnry Member

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    Check the wire gauge size before testing with 40 amp breaker..don't want melted wires..Also, check refrigeration head pressure ..chillers in parrell will operate differently when the load is light..check that you've are getting the temp differential out of your coils too across the range..clogged/dirty coils (air or freon)give this symptom as well..even with vsd..let us know please good luck
  12. Pascal

    Pascal Senior Member

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    I m going to be lowering the breaker rating so no risk of melting any wire

    Pressures were checked recently, after cleaning the raw water side and were fine.

    After running on just chillers 2 and 3 for 18 hours, I restarted nr 1. After 20 minutes the breaker for 1 and 2 tripped. I was in the ER re inspecting everything again. Breaker just tripped without any external indications like a noise or anything. Overall amps had been holding steady before tripping.

    now running on chillers 1 & 3
  13. johnnry

    johnnry Member

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    Ok sorry thought someone had suggested replacing a 30 amp breaker with a 40 amp ..so how is temp differential on the actual air side? U seeing a 15-20 degree or so air temp differential ?
  14. mapism

    mapism Senior Member

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    Which part of "you could replace the 40A breakers with 30A ones" in my post #2 was confusing enough to understand the opposite? o_O
  15. Pascal

    Pascal Senior Member

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    I don’t have to measure the air temp at the air handler... with chillers the loop temp tells the story.

    with all three chillers it comes back down to between 49 and 52 degree depending on the time of the day and sun

    on two chillers it doesn’t drop below 60 in the afternoon. Not low enough to really cool the boat as it should.
  16. Capt J

    Capt J Senior Member

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    Is it possible that the chiller set points are too low and causing the freon to freeze in the chiller?
  17. leeky

    leeky Senior Member

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    It's your accent.:D
    chesapeake46 likes this.
  18. Donzi 54

    Donzi 54 Member

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    Make sure that they are not cycling on together. Mine cycle on in rotation so as to not create a overload condition. Start amps are at their max at start up. Actually a loose connection shouldn't cause higher amp flow. Current drops with resistance, although the loose connection will build heat at that point
  19. mapism

    mapism Senior Member

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    Guilty as charged, your Honor! :)
  20. Pascal

    Pascal Senior Member

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    No they re at 49 or 50.