proximity issues

[r404a]

Chiller guys and gals,
Got a couple of questions about proximity sensors. I did a rebuild on a York machine, 1200 ton R22 centrifugal and the prompting was that the machine went out on "95 mils" proximity and further investigation showed a highspeed bearing melted to the shaft. Anyhow, this machine was rebuilt and I installed a new prox sensor and we lit the machine off. I never changed any programing or anything in the Micropanel.
The reason I am bringing this up is that this weekend I got a call for a TOTALLY DIFFERENT centrifugal machine, this is a 1000 ton R134a machine, that was out on proximity fault. The panel readout showed the proximity at 36 mils and the information that I found on this Micro says 37 to 79 mils is normal/accepted. Now, here is a bit of background: Supposedly this failure has happened quite frequently on this machine. I have been told that this happens when power failure occurs. I recommended to the supervisor of this property that this machine be inspected, but was told, in no uncertain terms, to recal the proximity sensor to get the machine online. I did this and the machine is online.
Thanks for the patience, now for the questions. First, short of a full scale teardown, how do we arrive at a way of determining if the prox sensor is errant or if we have a highspeed thrust issue? Next, this R134a machine has a different style proximity sensor, in construction and actually has a type of "receiver-controller" it is wired to, with what looks like 24 vdc input and 5vdc circuit. Anyone have any troubleshooting advice/experience to share on this set up? Is set up required when installing a prox sensor and does the number of turns you actually thread the sensor in have anything to do with the installation? Finally, are proximity sensors used on any LOW PRESSURE units? Thank you for your responses.


R404a

[hw chiller man]

I have had trouble with prox sensors also this year. First a little background. When the chiller is first comissioned this sensor is calibrated thru the micro panel with the oil pump on. My testing has revealed that the reference position is usually the thrust position of the impeller. ( The impeller is in a position close to the suction elbow.) This reference is then locked into the micro's memory and any reading > +10 mils or > -20 mils from the reference position will shut the chiller down. These are the readings that are important and can be checked by running the oil pump in manual and checking the prox sensor position thru the display data button.
The last chiller that this occured on was an R22 machine where my initial testing remained outside these limits and the alarm could not be reset. The only way to inspect the thrust bearing is to recover refrigerant and get at the bearing thru the high speed cover. This cover contains a counterthrust bearing, the end of the high speed shaft is then visible. You can remove the thrust plate and then the thrust bearing is visible. On this particular chiller this bearing was wiped and belive it or not it is made with copper pads. The thrust can be rebuilt without getting into other internals and in fact is what was done on this chiller. We tested the low speed thrust which was in spec and decided on just a high speed repair at this time.
I have removed 2 proximity sensors this year and they were identical. One was installed with an O ring and one with pipe dope. I reinstalled both with pipe dope only and just past finger tight, you don't need to reef on these things.
One word of caution, I would never recalibrate the prox sensor after a safety shutdown without written approval from the owner of the chiller resolving me of any liability for the chiller.
With regards to your chiller shutting down on prox sensor safety on power failures, I am told by York mechanics that this can happen on larger tonnage chillers and in fact they are wiring in the vane actuator to give a soft stop (vanes go closed before chiller shuts down) on regular shutdowns to avoid this nuisance shutdown.
Hope this info helps, if you have any further questions or need clarification just ask.

regards.............wayno

[hw chiller man]

r404A, I forgot to mention that you should have done a recalibration of the proximity sensor after the rebuild before you started the chiller. This would have set a new reference position based on the new high speed thrust bearing assembly. You might still want to do it and compare the new REF position with the old REF position.

[r404a]

HW,
Thank you for your replies. I think that the Micropanel book speaks of a setup on new prox, but I am unsure of how to glean the original prox set point. Would this be on the original commissioning sheet? Thanks again for your help.

Thanks,
r404a

[hw chiller man]

Generally the original REF position is marked on the back side of the micro panel door during comissioning of the chiller. All my York chillers have this marked on the door. I know the York startup mechanic in my area and he is a good guy and does things by the book. If that REF position is not marked it should be available thru York service because it has to be recorded on their start up sheet. Whether they will give you the info is the question, up here in Canada it is like pulling teeth. Once the compressor has been rebuilt the old REF position is no longer valid.

good luck to you.............wayno

[hw chiller man]

r404a
Not sure of what you mean by glean. Are you asking how to obtain the readings on the micro panel and what is the REF position and what is the actual position? This info is easily obtained by holding the Dispaly Data button, the screen will scroll thru various parameters until it gets to the proximity line. The REF position displayed here should match the position as written on the panel. This REF position will be reset once a clibration is done.

regards.........wayno

[r404a]

HW,
Thank you again for your replies. I am going to get by the job and program the new Reference point. I appreciate all of the input. Actually, pulling teeth would be better than what we get down here in the US from York which is jack ****. Take care and thanks again.

r404a

[heaviwall]

the thrust bearing <hi-speed> is abig deal york may be leary of giving that out due to the fact of this thing may not have been properly inspected or reset if the new reference is not put in at start -up and the oil pump not run then you could be too far forward ortoofar back and it does not take long to wipe athrust out at the speed were turning with the soft shut down logic this have greatly reduced this problem at power failure at certain loads <vanes-open>will cause thewheel to go back on the pads onthrust bearing,at loss of gas flow so minimizing gas flow by only having the eye of the impeller getting gas thru closed vanes minimizes the wheel going back to wipe pads on thrust pads