Trane self-contained water cooled

[johnnyonetruck]

I checked a Trane SCWD....... self-contained unit yesterday that is tripping out on supply fan overload. It seems to trip on overload only when it is coming out of night set back. The unit is controlled by a Tracer system and is shut down at 5 P.M. and restarted at 5 A.M. It has no heat. The unit does have a night set back temp setpoint of 80*. I assume that the space does occasionally get that warm at night and the unit probably runs some during the set back period. This unit starts and stops fine when using the "auto local, auto remote, and stop/reset" rocker switch. It only appears to go out when Tracer brings it out of set back. The supply fan is on a freq drive and is set to ramp pretty slowly. I can't understand why this would occur either during night set back or when Tracer is bringing the unit out of night set back and no other time. I have manually started and stopped this unit with the rocker switch many many times and can not duplicate the overload trip that occurs when Tracer has control. Any help would be appreciated.

[weezer]

Are there other units on this building? If so is this particular unit breaking properly before ramp up? If it is fighting against positive pressure, that motor will overheat. Or Tracer might be going into occupy while vfd is running in night setback. If that isn't set up properly you'll end up with trips on drive or sometimes motor. Good luck hope that helps.

[johnnyonetruck]

Originally posted by weezer
Are there other units on this building? If so is this particular unit breaking properly before ramp up? If it is fighting against positive pressure, that motor will overheat. Or Tracer might be going into occupy while vfd is running in night setback. If that isn't set up properly you'll end up with trips on drive or sometimes motor. Good luck hope that helps.

Thx for the reply. There are other units in the building. I can only assume that it is breaking properly before ramp up as I have never seen it trip while I am there. All my testing never makes it trip. The VFD never trips. It is the UCM board that is sensing the trip and locking out. It might be trying to go occupied while the unit is running on occasion......not sure. I guess I could camp out there one night and watch it. The building maint tech changed out the CT on the motor leads before he called us. Thx again for the reply.

[bku46]

What is the unit diagnostic, if its fan fail, I had the same problem for 2 yrs, turned out to be wiring from fan proof switch on blower housing [pressure diff switch] I replaced the switch and problem persisted. I install a CT on the fan leg and ran wires directly to the board. Hasnt failed in 3 months.

[maxster]

this is typical of all VAV systems,when the unit is in NSB and runs to satisfy NSB setpoint either it be cooling or heating the VFD goes to full Hz and the VAVs dump making it a constant volume unit.the reason for the dump is to get as many air changes thru the unit to make the NSB setpoint.when the SP is made the unit actually shuts off again either in the heating or cooling mode and the boxes close off due to no air on the balancing rings and the control signal that got them to go full open.now the problem....unit does MWUP(or in this case cool down)same cycle as NSB but different setpoint,you make the setpoint and the control goes back on the VAVs to modulate most of the time to minimums thru each stat remembering you just heated up or did a cool down.before the VFD can go back to its signal for static setpoint it is still at full 60Hz but the VAVs are closing causing your trip.if the VFD is tripping on amps the decel can be made quicker and the accel can beadjusted also.if the Trane ucm is tripping hi-static SP bring it up.doing the rocker willn't give you a trip....you need to do a NSB or MWUP and simulate the CV mode 60Hz VFD, and TEE a DWYER on the staic tube coming to see the pressure build back to the 1U4.

[traneman1]

Seen that one too, I found that the fan reqest relay sticking. Not sure on the designator though. Also check to see if there is current draw when coming occupied. Rick

[maintmankc]

Does it have a supply damper that tracer is not controlling?

[ZeroCool]

I agree with the other guys, the relay that starts drive will hang when it gets old, but usually only see that after shutdown, next morn the unit is off because drive kept running after it was told to stop. If it is the ucm lockout and there are no diagnostics on the drive, it means its seeing amp draw when it shouldn't, or does not see it when it should or sees an overamp. Check the dip switch settings on motor overload if its the old 1u1, if its a square d 56 make sure current limit is enab and set to 0hz with fla set(matching dips)and stop set to free.That way if you lock the pully down it will not over amp or in your case, running it WFO. If that does not help swap 1u1 with other floor and see if problem follows board. I have replaced several in the past few years.

[johnnyonetruck]

Originally posted by maxster
this is typical of all VAV systems,when the unit is in NSB and runs to satisfy NSB setpoint either it be cooling or heating the VFD goes to full Hz and the VAVs dump making it a constant volume unit.the reason for the dump is to get as many air changes thru the unit to make the NSB setpoint.when the SP is made the unit actually shuts off again either in the heating or cooling mode and the boxes close off due to no air on the balancing rings and the control signal that got them to go full open.now the problem....unit does MWUP(or in this case cool down)same cycle as NSB but different setpoint,you make the setpoint and the control goes back on the VAVs to modulate most of the time to minimums thru each stat remembering you just heated up or did a cool down.before the VFD can go back to its signal for static setpoint it is still at full 60Hz but the VAVs are closing causing your trip.if the VFD is tripping on amps the decel can be made quicker and the accel can beadjusted also.if the Trane ucm is tripping hi-static SP bring it up.doing the rocker willn't give you a trip....you need to do a NSB or MWUP and simulate the CV mode 60Hz VFD, and TEE a DWYER on the staic tube coming to see the pressure build back to the 1U4.

Unit is tripping on supply fan overload, not high static. I think I understood you scenario to apply to a high static trip. Sorry if I am not correct here. The VFD does not trip. It is the UCM that trips and always on supply fan overload. I have never seen a high static trip on the unit. I will try the CV mode that takes place in NSB to see if the motor overamps at some point. In NSB I suppose it is possible that the motor is overamping, but the drive never catches it. It is always the UCM. There is a CT on the motor that feeds back to the UCM. Thanks to everyone for the replys.

[Edited by johnnyonetruck on 09-27-2004 at 09:49 AM]

[traneman1]

Hey Johnny, did you check the fan request relay? I would also check the 1U1 . The only things that will cause this is the 1U1 is seeing current draw when the machine is un occupied .I have had this happen varios times and it was one of the two things. Try swapping the 1U1 with another one in the building. That is how I found it to follow another unit. Rick

[maxster]

OH! now i got it...if the unit goes into that NSB or MWUP the VFD should only go to 60Hz check that,with ct in the picture going to the 1U1 your amp rise that trips is not coming from the CV mode during NSB/MWUP but as the boxes go back to control and the "static rise" off the full VFD at 60Hz is changing to occupied and control.check your amps on the leg the VFD dounut is on just coming out of NSB/MWUP and check the dip switch settings for that motor within the 1U1.check the nearest register too during the change-over to see if the noise is there also as the VAV modulates to controlled setting

[johnnyonetruck]

Thanks for all the replys. Sorry I have not responded......got sent out of town and just got back. I am going to check the building next week and will try the 1u1 swap if the request relay checks ok. Thanks again.

[R12rules]

Originally posted by maxster
OH! now i got it...if the unit goes into that NSB or MWUP the VFD should only go to 60Hz check that,with ct in the picture going to the 1U1 your amp rise that trips is not coming from the CV mode during NSB/MWUP but as the boxes go back to control and the "static rise" off the full VFD at 60Hz is changing to occupied and control.check your amps on the leg the VFD dounut is on just coming out of NSB/MWUP and check the dip switch settings for that motor within the 1U1.check the nearest register too during the change-over to see if the noise is there also as the VAV modulates to controlled setting

??? if I knew what all that munbo jumbo meant ... I'd need another five an hour just to feel satisfied about myself!
man you guys are speakin' another language to my ears.


....OH! Now I got it!!! ..... yeh right......