Issue with Trane screw compressor

zepfan

We are having an issue with a trane screw compressor that is locking out on "winding temp alarm" The model of the chiller, that the compressor is located in is a
M# RTUA 1254 YG01 R3d1. Made and installed in 2005. The machine is two circuit with circuit a online with no issues. The compressor with the issue starts up, but never switches over to the run contactor, The start contactor and shorting contactor stay energized, then the compressor locks out after about thirty seconds. The circuit that stays online shorting contactor drops out after about a second, and switches to the run contactor. The run and shorting contactor are mechanically latched, and can not both be energized at the same time. I am thinking that this may be causing the issue, and that the load/ unload function may also have something to do with it, but am up for any suggestions that anyone would have. We have done the maintenance on this chiller for several years, and replaced minor parts. The system is air cooled with all fans operating, and the condenser coil was cleaned three weeks ago. Thanks to all

109A_5

Hello @zepfan,
Hopefully this manual is close enough for valid information of your equipment.
https://www.kigsales.com/specsheets/Trane_RTUA_and_RTWA_installation_manual.pdf
Not really sure if you are having a problem with the Lead or the Lag compressor. In either case it looks like the Starter Transition should be 1.6 seconds. I would chase back why that Starter Transition is not happening. There is wiring diagrams in the manual.

ratio

It looks like a Y start Δ run configuration. Since the contactors are mechanically interlocked, if one doesn't drop out the other can't pull in. Do the outputs do what they're supposed to i.e start contactor is deenergized & then the run contactor is energized? Are the current transducers reliable? If it's looking to make the transition based on current draw, it might be confused if they were out of cal.

Jamie Hall

ratio said:

It looks like a Y start Δ run configuration. Since the contactors are mechanically interlocked, if one doesn't drop out the other can't pull in. Do the outputs do what they're supposed to i.e start contactor is deenergized & then the run contactor is energized? Are the current transducers reliable? If it's looking to make the transition based on current draw, it might be confused if they were out of cal.

Sor of what I'm thinking, with my limited knowledge. What is telling the contactors to switch? Unlikely to be a simple timer, nor yet a centrifugal switch. Something in that current sensing controller...

109A_5

Hello @zepfan,

zepfan said:

The compressor with the issue starts up, but never switches over to the run contactor, The start contactor and shorting contactor stay energized, then the compressor locks out after about thirty seconds.

You have to find what is missing in this sequence or where the sequence stops. Does item 6 or 7 happen ?


1) 1U4 call for compressor to start
2) 1K3 is energized (Shorting contactor) via 1K2 Aux 2 and 1K4 Aux 1
3) 1K3 Aux 1 closes, 1K3 Aux 2 opens
4) 1K1 is energized (Start contactor)
5) 1K1 Aux 1 closes (1k1 is latched on)
6) After 1.6 seconds and / or current ramp K2 closes (1U4)
7) 1K4 is energized (Transition contactor)
8) 1K4 Aux 1 opens
9) 1K3 is de-energized (Shorting contactor)
10) 1K3 Aux 1 opens, 1K3 Aux 2 closes
11) 1K2 is energized (Run contactor)
12) 1K2 Aux 1 closes (1K2 is latched on), 1K2 Aux 2 opens, 1K2 Aux 3 closes (1U4 Transition Complete)
13) 1K4 is de-energized (Transition contactor)

zepfan

thanks to all that responded. This is all very helpful. I plan to go by the building the first part of the week, armed with the information above, I hope to figure it out

109A_5

Hello @zepfan,
I would verify the compressor current is close to equal on all three phases if you have not yet. Then I think I would check if K2 ever closes ( J7-5 to J7-6 ) at 1U4 or 1U5. If needed maybe 1U4 and 1U5 could be swapped, note the DIP switch settings ( DIP switches can oxidize with time, I would not change the settings if you don't have to).

If K2 closes is 1K4 (or 1K8) coil open ?

109A_5

Hello @zepfan,
After a bit more thought... What you may be experiencing may be a (more or less) normal protection strategy. I believe the compressor motor is cooled by the refrigerant, so you don't want the windings burning up and contaminating the system (if avoidable). So if the Current between phases has too much differential the Current monitoring system may let the starting process fail (by never closing K2, and then de-energizing J7-3). Since it only seems to monitor the Current to the compressor motor and not the Voltage at the compressor motor, there is a window of opportunity for the Current to become normal, and if not it errors out.

If you have not yet checked, I would check the Current and the Voltage at the compressor motor. The compressor motor may have a defective winding or one of the contactors may have a bad contact or there is a poor wiring connection somewhere.

zepfan

@109A_5 thanks so much for your response. The motor is refrigerant cooled, with the strange part being is that when the compressor shuts off on “winding temp” the temperature of the compressor is cool to touch. Probably 85-100 degrees cooler then the one that remains online. Thanks again I am going to do some more checking

109A_5

Hello @zepfan,
I did not look too hard, I did not see a temperature sensor. So I am running with the theory that the motor controller logic perceives a Current imbalance (actual or erroneous) or a motor starting contactor sequence failure issue and uses the "winding temp" error as a generic error, and it may not be from actual measured winding temperature rise. So it is a bit confusing. 3 phase motors with phase (Voltage / Current) imbalances can overheat.

Or the temperature sensor is buried inside the motor (are there actual wires for an internal sensor ?) and the winding temperature rise is so fast that the housing barely has time to warm up before the lockout happens.

Since it is starting in Wye mode I don't think the windings would actually heat up that fast, especially since you believe the motor is actually spinning.

What you need to determine is, what is interrupting or stopping the starting process.

1) Is the compressor motor defective (Voltage is good at the motor, current is not balanced).
2) Is there a bad wiring connection or bad contactor contact main or auxiliary. Voltage to the motor is not balanced causing a Current imbalance. High auxiliary contact resistance. Open contactor coil.
3) Current sensor issue, causing the erroneous Current measurements and thus erroneous behavior.
4) Defective motor winding temperature sensor (if it even exists).

109A_5

Hello @zepfan,

Found the winding temperature sensors. The odd thing is the extended and incomplete starting sequence.



Another thing I would check to help confirm the motor's integrity. If all the phase Voltages are within the 2% to the unit per the manual page 119 and 124 (no phase balance error). The Voltage to the unit may be OK but if there is a bad contactor the Voltage to the motor may be beyond 2%. I would check the Wye common point wire at the Shorting contactor during the extended starting time.
Example;
460 / the square root of 3 (1.732) = 266 Volts
480 / the square root of 3 (1.732) = 277 Volts
Any and / or all phases to the wire between the shorting contactor connections. I would measure the Line side and the motor side of the Start contactor. You can also measure the Voltage if any across each contact of the Start contactor and the Shorting contactor.

clammy

Not to sound foolish ,is there enough for a td to allow for the unit to operate and is the call for it to operate still engaged after it locks out ? Have you tried to switch the properly operating unit off and have the one w the issue carry the load to be sure that the unit isn’t just cycling off due to a narrow td across the water side of the plate . Could there be an issue on the chilled water side of the plate causing the unit to not full engage into a run cycle. Again not to sound foolish has anyone put a set of gauges on the unit to chk the charge and aside from a eev does the unit have a separate liquid line solenoid ? Just shooting some ideas it’s been a long time since I ve worked on any process chilled water and only worked on one screw system and it was a hitachi most where carrier semi hermetics and the last few where w plates no eev . Old shell and tubes had less issues and where more forgiving it seems that there where always some issues w plates either on ref side or water side now most are air cooled being no likes tower maintenance and the so called nonsense but either way the coil or tower always need attention aside from indoor strainers . Peace and good luck clammy

zepfan

thanks to all that responded. We have been short handed this week so I have not had a chance to get back to this building. The other circuit keeps the building online, although this is working with out a net. As soon as I get a chance to go back by, I will report back as to what I find. Thanks to all again

zepfan

It turned out the compressor module was defective. The transition contactor never would energize, therefore the shorting contactor stayed energized the entire time, and then the compressor would lock out on winding temperature.

It took a while to get approval from the customer to change the module, then a while to get the part. I replaced the module today, and both compressors are online now. Big thanks to all that commented, and an especially huge thank you to @109A_5 breaking down the starting sequence was very, very helpful. Thanks and take care to all