View Full Version : McQuay Centifugal
03-09-2005, 09:08 PM
Chiller guys and gals
This is one that has been going on for a little while....McQuay R134a machine, Model# PEH087-AAAB
Serial number S7B81030-00. About 2 or so years ago, the shop got a call on this machine. A tech went out, L1 and L2 600 amp fuses blown. Replaced. Ran for a couple of months. Another tech goes out, L1 and L2 fuses blown. Replaced. This happened a couple more times and I inherited the issue. I cannot say what they found and they have long since left the shop. So, around Nov of 2003, I get my first call on this machine, and by now, I am sure that you have guessed the call.... thats right, L1 and L2 fuses blown. I meggered the motor to ground, showing at or close to infinity,with no phase to phase shorts, checked wires and physical interlock, etc. I did decide to order and change the shorting contactor points, and ran the machine.Didn't have a problem with this machine(that I know of) until recently, when maintenance was being done on the tower and I caught hell trying to get it online with very cold tower water. I made a point to ask the facilities director if the fuses had blown since that last call and he indicated that they had not had a recurrance of this issue....until this morning. So, I get there and L1 and L2 are blown, megger as stated above and check the physical interlock between 1S and 2M, as I did before. I am going to replace it and the other AUX contactors in the course of my trouble shooting and would like some input. Thanks.
03-09-2005, 09:26 PM
after it runs a while i would check the fuse and wiring with a infrared thermometer to look for hot spots as a poor connection. i would go back to the main breaker also. also you can put a voltage recorder on and see what is happening over time.
03-09-2005, 09:28 PM
I think thta is a good idea. I will get the data logger and try it out. The infrequency is what has me going.
03-09-2005, 09:34 PM
I do have one thing to say about your megger, if that's as good a reading as you can get, you should maybe get a different one.
Having said that, you could always rotate L1 to L2, L2 to L3, then L3 to L1. This will keep everything in same rotation. If problem follows your moves then it's a line problem.
High amps can be caused by low voltage on the feed. I'd check with utility and see if they had problems on particular days.
Last but not least are the fuses sized properly?
Eventually whatever is causing the problem will release its encapsulated smoke and you will be able to locate the problem.
[Edited by r718 on 03-09-2005 at 09:39 PM]
03-09-2005, 10:08 PM
good idea on the switching of lines. thanks.
03-10-2005, 03:21 PM
I don`t know how they prove vane closed at startup with Microtech are they still using vane closed oil pressure switch? Could be sometimes starting with vanes partially open or a bouncing flow switch. Just a thought...
03-11-2005, 06:16 PM
Hold it hold it "Timmy or Jimmy" think about the advice on switching L1 L2 - the compressor will only run in one direction!!!!!!!
03-11-2005, 08:19 PM
Yep, ya always got to think about what you read on the internet.
I guess it's possible if ya switch the line side as follows; L1 to L2, L2 to L3, L3 to L1, that the compressor may change rotation. I'm just not sure on what planet.
03-11-2005, 08:34 PM
Make sure that your wire size is correct for your machine and length of run from electrical room, it could be sized so close that at high load conditions it over amps the fuses, it could also be a short in the wire running back on the line side.
03-11-2005, 11:24 PM
Appreciate all of the input. Mathias, I did put a rotation meter on the machine and have not started it yet, I will let the oil warm up first. Like I stated before, I have not had much experience with this style machine and I know LEW2 has,among others. How does this machine assure oil return? I have a unit adjacent this one with a low level of oil in the tank, and I ran it overnight. I have a five degree evap aprroach, 2 degree suction superheat and very little discharge superheat, so I know that charge is not an issue. Today my sump is still low. I put a call in today to get an O/M manual on the machine so I can get a bit more edu-macated
03-12-2005, 09:17 AM
I have a question, and some suggestions..... is the starter fused? Or, fuses in distribution panel? If fused remotely, I might suspect L1 and L2 get together on occasion. It is also possible that there is an intermittent short between T1 and T2 in the conduit. Next, I would turn off the liquid injection to the compressor and check discharge superheat. It should be around 14 degrees at full load, and go up from there as the load decreases. From the refrigerant side, I suspect the compressor may be seriously flooding back at start-up, although I don't see why it would always pick L1 & L2 fuses to blow. You might also test the vane closed switch for calibration. I would set it to 40 psid. Finally, look closely at the motor terminals for cracks and copper spattering. Thismay be a path to ground, especially when they start sweating.
03-12-2005, 09:53 AM
Look for device that is single phase running on L1 & L2 only. Control power transformer, pump motor, etc.
03-12-2005, 10:40 AM
Check RMS rating on replacement fuses, it may be to low.
03-13-2005, 10:01 AM
May be wrong rating
03-13-2005, 12:19 PM
These are all good inputs. I am goimg to follow up on them tomorrow. Thanks.
03-15-2005, 09:51 PM
How about capacitors, any and are they Ok?
What did you find?
03-17-2005, 11:04 PM
Still have not gotten back to this job yet. Started it up and checked charge after changing 1S and 2M interlock. No capacitors on this one, do have a surge suppresor on the line at the compressor.Thanks for all of the inputs and I hope that I can get back on this one soon.
04-02-2005, 03:10 AM
Try doing a dry run test a couple of time and check the tightness of all the three phase wiring. I agree with the data logger. Check auxilaries on contactors and test. replace auxilaries if needed..............
04-03-2005, 01:37 AM
If this machine is a retrofit from 12 to 134, then good luck.Used to have 2 of these that were smaller. Must watch discharge & suction superheat VERY CLOSELY. They were not good candidates for retrofits in my opinion.On start-up with warm water temps, you may notice liquid entering the suction side of the impeller.When this happens you will not feel warm & fuzzy,because it can not take this for long.Had major oil return problems with the ones that I had and it was amplified at low loads. Factory support for the problems that I encountered was non-exsistant.
I would be curious if it was over amping on start-up after shutdown, due to relatively high load. Be real careful & move slowly when adjusting super-heat on these machines.If you do get liquid entering the impeller, the amps do jump way up.But it will not do this for long. High speed pinion & bearing assembly impeller is gonna start at about 20 grand.
04-04-2005, 08:54 PM
Check the MCC for load balance and voltage variations.
04-05-2005, 03:29 PM
I'm assuming this machine came from the factory charged with 134A if not and it was retrofitted cut o rings in the front end could be a problem. Check your oil vent pressure with the machine near full load, this can be done with a gauge on the center line of the oil pot, there should be a 1/4 flare on this line for that purpose. This pressure should be 2-3# below your actual suction (measure you actual suction with the same gauge) if it above suction pressure by more than 5#'s you are pressurizing the oil sump and preventing the oil from draining back freely. Possibilitieis: cut o ring in front end, bad high speed seal, cut orings in high speed assmembly, bad o rings on low speed bearings. McQuay has a guide for test oil loss in there manuals suggest you get a hold of it and use it.
04-05-2005, 06:06 PM
R and R,
Yes, this is a 134a machine, not retrofitted. I will also check these things. Do you think oil loss could cause an over amp situation like this? Thanks for all of you inputs.
04-05-2005, 08:50 PM
No, oil loss will not cause the over amp condition you are describing. You could get some amp flucuations if you were grossly over charged with oil, and it was flooding back to the impeller (similar but different to refrig. floodback).
Does the unit continue to lose oil? Or, is the level just low? Starting the chiller with excessively cold tower water is one way to lose some oil, which may not be recovered. If it is simply low, add to at least 2/3 full sump. Mark it and monitor. If it does lose oil, then the procedures that ruglenr suggests will be in order. Bob
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