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  1. #1
    Join Date
    Mar 2004
    Location
    Windsor ON Canada
    Posts
    402
    I was called in today to inspect this particular chiller. Trouble happened on Saturday. At approx 9AM the master compressor went into an alarm condition "Suction temp sensor failure". AT this point the compressor should have shut down but did not. It appears by reviewing the Alarm logs that the compressor ran in an unloaded condition for another hour before the operator pulled the disconnect to shut the compressor down. The lag compressor was also running during this time which was keeping the pumps on and the refrigerant pressures in the proper ranges. The alarm logs before shutdown indicate a discharge temp of 260F, a suction temp of 248F, oil sump temp of 166F and oil supply temp of 125F. Was able to determine that the Cutler Hammer soft start is the problem. Entered service test mode and started the oil pump, quickly threw the disconnect while the compressor is still in alarm mode and the compressor started. It was immediately shut down. The Cutler Hammer issue is going to be addressed tomorrow by others. I, however have a couple of concerns with respect to running this compressor after this situation. What type of damage if any may have been caused. I did not hear any unusual noises during the brief period that the compressor ran. I was considering running the compressor and have a vibration specialist check it. Also after reviewing McQuay info I cannot determine what kept the oil pump on. All thoughts will be appreciated.

  2. #2
    Join Date
    Feb 2002
    Posts
    180
    If your saying that the soft start failed to shut motor down then the micro would have seen motor current and kept oil pump running. Hope thats what you were looking for.

  3. #3
    Not good, not good at all. The oil pump, as 787 guy stated, will continue to run as long as the MT sees current being drawn by the compressor. Never saw your situation happen with the soft start starter. I would like to know what you find. Those extreme temps. worry me. An oil AND refrig. sample should be taken and analysis should definetly be done. I'd almost lean towards an internal inspection as well. I'm not sure what the max temps. would be for the suction victaulics and O-rings.

  4. #4
    Join Date
    Feb 2003
    Location
    Wichita Ks
    Posts
    1,399
    i hope the impeller is ok. if the other compressor was working ok and the lead was unloaded then it probally did not open the check valve so the impeller was free spinning. if this does it long enough it will melt. i have seen this happen on dual compressor units. controls will need to be test completly by some one who knows it.

  5. #5
    Join Date
    Mar 2004
    Location
    Windsor ON Canada
    Posts
    402
    The suction victaulic and the gasket on both sides of the suction damper is leaking. The starter was definitely shorted closed. The Cutler Hammer rep advises that heat in the starter cabinets is a big issue with these starters. Excessive heat will cause the SCR's to fail closed and excessive current will cause them to fail open according to him. There is a dedvice on the starters that looks like a thick credit card where all the variables are set which is also affected by the heat. The CH rep has been to this site last year when a motor on a different chiller failed. It had an open SCR. At that time he advised the customer to install cooling fans in the starter cabinets of all the compressors but the customer would not go for it. At this time I still have not heard back from McQuay to see what there position is. Thanks for the info to 787 and bt, I was sure the micro was keeping the oil pump on but could not find verification of this in any McQuay literature.

  6. #6
    Join Date
    Aug 2003
    Location
    Baltimore area
    Posts
    1,818
    I can't help to much on your particullar problem but I CAN tell you that I have installed quite a few starter cooling fans in the same chillers you have . McQ has a part # for the kit.

  7. #7
    Join Date
    Apr 2004
    Posts
    423
    Well you need to isolate that comp and remove the suction elbow and atlest check to see if there is even an impeller left. when you ran the oil pump did it build up pressure? is the oil clear? replace the butterfly valve if it is leaking.

    What your telling us happen dosen't make sense if the unit was off on alarm (bad suction temp sensor) and the comp was still running( bad starter) then the oil pump would NOT have been running. it would have gone into a post lube after the alarm and would have quit. your info is false or what you think happened is false. either way to be safe remove the suction line and inspect it. and if it needs rebuilding call McQuay Service!

  8. #8
    Join Date
    Mar 2004
    Location
    Windsor ON Canada
    Posts
    402
    Chilly, with all due respect two other posters have already stated that the micro will keep the oil pump on if it sees current draw from the compressor. McQuay literature does not specifically state this, so that is why I asked the question. The alarm logs indicated that oil pump was on due to the oil pressure that existed. When the operator pulled the disconnect the oil pressure immediately reverted to suction pressure so I am positive that the pump was on for duration of the incident. When I ran the oil pump after the incident it produced proper pressure. The oil analysis is not back yet but the oil did not look discolored when I took the sample. The leaking suction elbow joints will be repaired and a visual done of the impeller. When this will happen I am not sure because the customer needs the other compressor at this time. If further repairs are needed then we will quote the work.

  9. #9
    Join Date
    Feb 2002
    Posts
    180
    I was thinking the sequence of events was more like the compressor tried to cycle off but starter problem prevented motor from stopping THEN all the sensor failure alarms happened. I was thinking the suction temp failure was due to sensor being out of range and you should have had a high discharge temp alarm. The initial alarm I think would have related to motor current present with comp off. What was in the alarm buffers?Were they loaded with temperature related alarms possibly purging an initial alarm?

  10. #10
    Join Date
    Mar 2004
    Location
    Windsor ON Canada
    Posts
    402
    Thanks 787. The last alarm log in the buffer (No.8) was the suction sensor failure yet the temperature for the sensor at that time was at 248F. And yes there were a number of duplicate alarms that may have overwritten the initial alarm. Because the alarm could not be cleared after the incident and was still reading 248F, the sensor was replaced and I was able to clear the alarm. At some point the sensor did fail. Whether this caused the sequence of alarms or became part of the sequence is a very good question. No other alarms were ever annunciated except the suction failure temperature alarm. There were no remaining alarms in the buffer indicating any problem with the motor and the operator could only recall seeing the sensor failure alarm.

  11. #11
    Join Date
    Nov 2004
    Location
    North Florida/South Georgia
    Posts
    983
    Hey chilly, do you work for McQuay?
    All my leon freaked out!

  12. #12
    Join Date
    Mar 2004
    Location
    Windsor ON Canada
    Posts
    402
    Just a follow up on this incident. The oil sample came back and was good. The oil pump was started and produced proper pressure with no oil loss. The starter was replaced by Cutler Hammer and the compressor was started. It has been running continuously for one month now. Oil level is good and all operating parameters appear normal. Once the compressor can be shut down, the small leaks will be repaired. Thanks to all for their imput.

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