Hey guys an easy way to check the gas pump operation is to watch the discharge superheat, when the drain valve is energized the superheat will drop a few degrees and of course it will go back up when the fill valve is energized the temp differance takes about a min. or two and you could do it without techveiw because the ch-530 shows the discharge superheat.This is the first thing I do to check the gas pump,before moveing to the oil level sump eye which is easy to check out also,And I agree DON'T ADD OIL unless you see a puddle under the machine and then you other problems too.
Thanks BKLYBORN for your response . I never considerd doing that but it makes sense . Would you mind sharing on how you check the oil level sensor ?
Originally Posted by BKLYNBORN
Not with the company anymore so I do not know what the progress is . I believe I heard that they were still haveing problems after the check valve was replaced . If that were the case , my next concern would be the load and unload cylinder seals etc . Would that be the next suspect issue to investigate ?? Given that the gas pump operation was verified via the discharge superheat method .
Yea to check the oil level eye is simple it is located on the sump on the control panel side thier is a snapring that needs to be removed and the eye will come out and yes it is a dry well.When it is out cover it with black eletrical tape it should read DRY if not it is bad,and sorry I forgot you want to do this with the chiller OFF.Make sure it is put back all the way in and the snapring is back in place after these two checks I go into actuall oil level the way Graham said and move oil back into the sump from the evap which is slow and painfull.And the few times I have had this problem it has been one of these two things it is a pretty simple way for the machine to return oil with the falling film evap.And it sounds like that company should call Trane to check it out if this problem still is happening,because lord only knows how much oil is in their now
I have two RTHD chillers in the same plant. One has problems with loss of oil about twice a year. The other has never had a problem. The gas pump always checks out fine using the discharge superheat method. The original installer could not figure it out. Local Trane techs have looked at it several times and say they are stumped as well.
I thought that I fixed the problem a couple years ago when I replaced the master oil solenoid. When the machine shuts down you can hear oil flow through the oil sump if you carefully put your ear to it. If you close one of the ball valves on the oil feed line the sound stops. Open valve sound starts again. Seemed like the solenoid was leaking by. Discharge pressure would push oil out of the sump and into the compressor. Replaced the solenoid. Sound was still there but seemed better and ran for a year or two without a problem. Anybody else notice the oil flow sound after shutdown? Any other explanation other than oil flow?
I will request the service bulletin on Monday as a Google search did not reveal anything helpfull. Figured we would just have to live with this problem.
The oil and refrigerant charge are all correct. A really good tech from the factory pulled both when he changed out the liquid level sensor and weighed all back in. I always pump the bottom of the evaporator into the oil sump to return the oil.
One has problems with loss of oil about twice a year
What kind of condenser water temp control do you have . Do you have a three way valve on the tower ??
Have you replaced the gas pump check valve ??
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It has good water temperature control. Two towers with VFD's on the fans provide very stable water temperature. This system never shuts down so the condenser temperature is alway constant. The system uses a smaller "pony" chiller year round. The pony chiller has a condenser water bypass to control it's temperature if it should ever have a cold start.
The RTHD's are staged on as needed for a total of 5 stages of chiller when run with the pony chiller. Chilled water flow is calculated and pump VFD's and bypass valves adjust to ensure documented correct chilled water flow through each chiller. It is a pretty complicated sytem.
I have never seen a reason to replace the gas pump check valve. It always seems to work fine. Is this what the above mentioned service bulletin addresses? Sorry for asking before I have requested the bulletin from our local Trane office.
The shut downs do seem to happen on start up. Chiller could be off for a cycle or for monnths. That is why the leakage on shutdown made sense to me.
Thanks for the response
Just need to ask a stupid question someone has checked the sump heaters and oil temp while it has been off for a long time right.And what do you do to get it running again? Servicetech 32
No stupid questions, just stupid answers.
Originally Posted by BKLYNBORN
Both sump heaters work fine and the sump is always nice and warm. The chillers are in a conditioned mechanical room.
To get it going I use either a liquid transfer pump or a recovery machine to move liquid/oil off the bottom of the evaporator until the oil sensor shows "wet" and then a little longer. I do find that the transfer pump can and does overwhelm the oil sump heaters so when I did it this way I would need to wait a day for the heaters to boil out the refrigerant before I can start the unit. Now I say slower is better.
Servicetech 32, Sounds more like you have an oil migration issue than an oil loss problem as your oil loss diagnostic is occurring on start up following an extended shutdown. If you had a master solenoid problem you would more likely be experiencing “loss of oil – compressor stopped” diagnostics.
POE lubricant’s are chemically engineered for a strong molecular attraction to the refrigerant. The advatage is this bonding helps overcome oil return issues but a downside is oil migration can occur if external conditions cause thermal movement of the refrigerant charge. For this reason RTHD chillers ship with oil sump vent line valve closed to reduce solar induced refrigeration migration during shipment
The oil sump vent line valve is then opened when the chiller is commissioned but if the chiller is subject to temperature swings in the off mode refrigerant charge migration can occur in such quantities that the sump heaters cannot prevent washout of oil from the sump. If the temperature in the evaporator is allowed to cyclically exceed the temperature in the condenser you will have problems with oil migration regardless of the operation of the sump heaters.
We have sites where weekly operation of the condenser water pump for chemical dosing circulation with the chillers off has caused oil charge loss through refrigerant migration. The chemical circulation was necessary for corrosion control so while it may not of been a “factory fix” to overcome the problem on affected sites have installed a solenoid valve (normally open for fail safe operation) to the oil sump vent line that is energized closed whenever the chiller is off. Have also experienced oil migration issues in cooler climates where the plant room is open to the ambient temperatures which has been corrected with the addition of the vent line solenoid.
Only thing I can't figure is why it would occur on one chiller and not the other - could be site configuration related
Last edited by Screwit; 10-03-2010 at 12:39 AM.
Reason: Simple fridgee who can't spell very well
You have made some very good comments and seem very educated. This plant does cycle the condenser valves on a weekly basis for the same reasons you describe as I recall. The condenser water temperature would be about 5 degrees warmer than the ambient room temperature that the chillers are in. I will give this some thought.
My question would be why would one chiller be effected and not the other? Both sit in the same room and experience the same chemical treatment cycle.
You speak of oil sump vent lines. Our chillers oil sumps vent two ways. One is through the master oil solenoid valve and the other through the oil separators. It seems hard to imagine oil filling the oil separators to the point that the oil itself would float out of them and into the condenser. I have witnessed it is possible with enough flow from a liquid pump from the evaporator to the oil sump to cause this so I guess it may be possible. That is why I think slower is better. You have given me some things to think about and I thank you for that.
RTHD chillers also have an oil sump vent line from the top of the oil sump to a valve on top of the condenser with the purpose of venting the oil sump to the condenser to prevent a vapor lock of the oil sump, the isolating valve on this vent line ships closed.
I am also scratching my head why only one chiller on a site would be affected by refrigerant migration caused oil loss but it could be due to the configuration of the site, plant operating sequence, chiller size (if they are not identical) or for reasons other than the above.
The root cause of the refrigerant/oil migration problem is the micisbility of the POE lubricant and the R134a even when in vapor form, when temperature changes occurs refrigerant migrates through the system and carries the oil with it - having the oil sump vent line closed helps prevent refrigerant migrating through the oil sump and the resulting oil migration as the refrigerant is boiled out.
Last edited by Screwit; 10-04-2010 at 12:31 AM.
hey bud, do u think i could get that demo? thanks
Originally Posted by maxpower
You don't control chiller plant call or stage up do you . See if chw pumps are running on or starting when they shouldnt be. Oil sump on rthd sits above cooler vessel.????
Originally Posted by servicetech 32
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