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  1. #1
    Over the past month we have replaced 3 compressors on the same Trane rooftop unit. The 20-ton unit has two compressors and the same compressor has blown three times in a row. Since the unit is 20 years old initially the compressor was thought to have died from natural causes. But when the second one was blown our technicians proclaimed that there was an electrical problem, because the contractor had locked out. Con Edison was brought in to inspect if there had been any spikes, they found nothing wrong. After we noticed that the unit had tripped we called our HVAC service to let them know that then 3-day-old compressor may have just died again. Much to my dismay we found that the new compressor had blow. A recent theory from our technician is the electrical problem is from the phase monitor. Is it possible that the phase monitor has been the source of the problem?

  2. #2
    Join Date
    Oct 2001
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    6,966

    Hmm

    do you have a model on the unit,the phase monitor if as shipped from Trane is inside the reset circuit so the unit should of locked out on an amp spike or brown out situation,are the compressors across the line or PWS on the contactors?if your condensers are dirty within but are surface clean that will trip the module.

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,357
    If you've already eaten three compressors, makes me wonder how good of a system clean-up the techs are doing between changeouts.

    Your post indicates you may be a building owner or manager vs. a tech, but as such I would be curious as to how well the cause of the original compressor's failure was investigated. So many times when a compressor burns out, it's changed with a poor to fair cleanup procedure, and that's it. The standing assumption is that the thing just died and the new one is the solution. BAD ASSUMPTION!

    The overall condition of your system should be assessed. Airflow, coil and blower cleanliness, air filters changed religiously, refrigerant charge, etc. Voltage supply, integrity of all wiring, including what supplies power to the unit, etc.

    To answer your question directly, I've never heard of a phase monitor taking out a compressor. I have one each on both of my large split systems and have had no problems with them. Last year one of them tended to trip, reporting "phase loss" each time, which probably saved the compressor. This year's been smooth sailing. I would not remove these monitors unless somebody could prove to me they kill compressors.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Yes I am a building manager and this old building/HVAC system has lost several compressors over the past few years. The units are maintained regularly and we have our contractually seasonal full check up on everything. Which is not to say that the techs might have done something haphazardly, however with the amount of different people who have been here I would be shocked if something that small was overlooked. The fact that the second stage compressor has blown out 3 consecutive times in the past month is troubling. On two occasions we know for certain that the unit tripped. If the phase monitors tripped the unit to protect it from a spike why are the compressors still grounding out?

    The last report speculated that the phase monitor was “bleeding voltage to compressor causing windings to heat up and overload causing grounding, must contact manufacturer.”

    It seems typical to blame the manufacturer, but can a phase monitor ground out the compressor by “bleeding voltage?”

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,357
    The fact that the second stage compressor has blown out 3 consecutive times in the past month is troubling.
    "Second stage compressor"? Are we talking about a tandem compressor arrangement, where both compressors share the same refrigerant charge, same evap and condenser coils, same oil? Or is it on a separate circuit?

    If the tech suspects the phase monitor, why doesn't he change it out for a different one along with the compressor? A different brand if he ain't keen on the one in your unit?

    Seems to me if there was any "voltage bleeding" of any significance occuring through this monitor between the lines, you'd have a short and the breaker would trip or diconnect fuse blow. The phase monitors I'm familiar with don't feed line voltage through them directly, but are wired in parallel to the compressor contactor line and load sides. Any "voltage bleeding" of any significance between any two of the three lines would in my mind be a direct short.

    I would ask the "bleeding voltage" tech to define his terms. Have him draw it out on paper. If he balks or fumbles around, he may not really have the answer. Of course he might be a good BS artist and concoct some wild theory out of his behind to cover same. Or...he might be right. But I just can't see it.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #6
    Join Date
    Oct 2003
    Location
    edgewood nm
    Posts
    73

    3 compressors

    Dear Penny Lane:
    Three compressors on same circuits in a few months? One question; are you paying each time or are they being replaced under warranty? As was stated by wisemen formerly, there is a reason for these failures. And the individuals who are replacing them are supposed to figure that out! In the past several years I have not seen nor heard of a phase monitor bleeding voltage. Any so-called leakage across phases will cause an immidiate blown fuse and or breaker. My advice to you is this: Put the brakes on these guys and get a second company to come in to thoroughly troubleshoot this system. Be forwarned, this might take as much as 8 hours to do. If you find that the first company bauched the thing have the second company do the repairs and send the bill to the first company. Good luck.

  7. #7
    Join Date
    Jun 2004
    Posts
    420
    A phase monitor should be breaking the control voltage the contactor, so there shouldn't be any possibility of "Bleed Voltage". I guess it's possible it could be chattering the contactor or something though.

  8. #8
    Join Date
    Sep 2000
    Location
    Miami, Fla. USA
    Posts
    417
    Originally posted by penny lane

    The last report speculated that the phase monitor was “bleeding voltage to compressor causing windings to heat up and overload causing grounding, must contact manufacturer.”
    Say Whaaat? This I gotta hear.

  9. #9
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579

    Phase monitors do not cause compressor failures. I know of no relationship between the phase monitor and the compressor that could result in a compressor loss.

    Compressors nearly always fail due to a system problem. When a compressor fails the replacement almost always fails unless the actual cause of the problem is located and rectified. I suspect that the actual cause of the first compressor failure was never actually determined.

    You don't need people guessing. You need a real professional to tear down the compressors and determine the actual cause of the failure. Tearing down a compressor does not void the compressor warranty. However, you also need the compressor failure investigated by someone who really knows how to perform a compressor failure analysis properly. An electrical failure of a compressor is not always caused by an electrical problem as the first cause.

    For example, flooded starts or liquid flood back can cause a loss of lubrication (refrigerant saturated oil is a poor lubricant). The loss of lubrication can cause main bearing wear which can cause the rotor to drop and scrape the stator. This in turn causes winding insulation to wear off and results in a motor burn and electrical failure including the possibility of a grounded compressor motor.

    There are other possibilities as well. I am just providing you with an example. Only a professional compressor failure analysis by an experienced professional will give you the answers you need.

    Few, very few, HVAC technicians know how to perform a careful failure analysis. Often they don't bother to tear the failed compressor down and if they do, they often are unable to follow the path of the failure to its ultimate cause.

    You may be best off if you ship one of the failed compressors to someone who knows what to look for and have them send you a report of their findings.

    It is still better if someone comes to your site and takes operating condition measurements of your system to check for refrigerant migration, liquid floodback, flooded starts, current and voltage imbalance, signs of overheating and more. It takes a bit of Sherlock Homes work that the standard HVAC technician is generally not able to perform.

    The cause can be determined and solutions found. But it can't be accomplished by a few posts.

    Norm

  10. #10
    Join Date
    Dec 2003
    Location
    Nevada
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    Had one that blew out a compressor because our controls contractr wired it into the compressor contactor. The unit has a liquid line solinoid valve controled by a seperate t-stat and a time delay wire in series with the time delay in the phase monitor eventually wired into the low press control for the compressor. When the compressor came on 20 min after the solinoid valve opened dumping liquid into the suction it blew it's valves. There were 5 compressors previously and since we rewired it there have been none for over 2 years.
    Quote
    “Engineers like to solve problems. If there are no problems handily available, they will create their own." Scott Adams

    "We can't solve problems by using the same kind of thinking we used when we created them."
    Albert Einstein

  11. #11
    Join Date
    Sep 2002
    Location
    South Dakota
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    6,579
    Originally posted by hvacbear
    Had one that blew out a compressor because our controls contractr wired it into the compressor contactor. The unit has a liquid line solinoid valve controled by a seperate t-stat and a time delay wire in series with the time delay in the phase monitor eventually wired into the low press control for the compressor. When the compressor came on 20 min after the solinoid valve opened dumping liquid into the suction it blew it's valves. There were 5 compressors previously and since we rewired it there have been none for over 2 years.
    Right, because you found the problem. But after 5 compressors just makes my point, few technicians are actually capable of performing a proper compressor failure analysis.

    I have been on a number of roofs where there were two or three old compressors still sitting next to the system and the compressor in the system had failed yet again. Not only were the technicians unable to find the problem, they did not even have it in them to remove the evidence of the previous failures. That made my job that much easier since I had several compressors to tear down. Yup! All of them had failed from the same ultimate cause.


  12. #12
    Join Date
    Nov 2002
    Location
    NJ - WORK IN NYC AREA
    Posts
    1,466

    Smile

    I would have to agree with weezer.
    "My hands are for sale"

  13. #13
    Join Date
    Dec 2003
    Location
    Nevada
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    1,815
    Originally posted by NormChris
    Originally posted by hvacbear
    Had one that blew out a compressor because our controls contractr wired it into the compressor contactor. The unit has a liquid line solinoid valve controled by a seperate t-stat and a time delay wire in series with the time delay in the phase monitor eventually wired into the low press control for the compressor. When the compressor came on 20 min after the solinoid valve opened dumping liquid into the suction it blew it's valves. There were 5 compressors previously and since we rewired it there have been none for over 2 years.
    Right, because you found the problem. But after 5 compressors just makes my point, few technicians are actually capable of performing a proper compressor failure analysis.

    I have been on a number of roofs where there were two or three old compressors still sitting next to the system and the compressor in the system had failed yet again. Not only were the technicians unable to find the problem, they did not even have it in them to remove the evidence of the previous failures. That made my job that much easier since I had several compressors to tear down. Yup! All of them had failed from the same ultimate cause.

    You've seen a compressor graveyard too?
    Quote
    “Engineers like to solve problems. If there are no problems handily available, they will create their own." Scott Adams

    "We can't solve problems by using the same kind of thinking we used when we created them."
    Albert Einstein

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