Trane TCD Cond Fan Fuses Blowing

[rgd2005]

My newly aquired customer has 4 of these package rooftop units,
Mod#TCD600AD0C2BBNF4DH
The 20 amp condenser fan fuses blow from time to time.I first
saw it happen this summer.
The motors ohm out good and draw
about 6 amps.Two (208vac/1 phase) motors per 20 amp fuse
(one 20 amp fuse per line)
I had another call on one of these yesterday where all 4 fuses were blown(all 4 fans offline).Replaced the fuses after checkingfor grounds,open windings and bad run capacitors.Motors came online without a hitch.

[stickinit2thman]

My newly aquired customer has 4 of these package rooftop units,
Mod#TCD600AD0C2BBNF4DH
The 20 amp condenser fan fuses blow from time to time.I first
saw it happen this summer.
The motors ohm out good and draw
about 6 amps.Two (208vac/1 phase) motors per 20 amp fuse
(one 20 amp fuse per line)
I had another call on one of these yesterday where all 4 fuses were blown(all 4 fans offline).Replaced the fuses after checkingfor grounds,open windings and bad run capacitors.Motors came online without a hitch.

Did you check start-up amps, are fans staged, are the fans not running spinning bacwards before start-up? Also check wiring, loose connectors ect. are bearings worn? can you pull or push on shaft and feel resistance? Ive had motors run fine untill a load is put on such as pulling/pushing effect of fan. check to see if any are turning backwards/is it 3ph? maybe someone replaced fan motor and didnt check rotation,also if not 3ph check caps. and wiring to them for misswiring.

[rgd2005]

I did check starting amps,voltage capacitors,wiring for shorts or miswiring.Nothing like these seems to surface.These motors are single phase and wired from the factory to run in the correct rotation.
They seem to have enough torque to change from deenergized
(turning backwards)to correct rotation when energized.
The fuse blowing problem seems to appear on all 4 rooftop units at various times.
The customer has been told that the electrical service to his building is bad at certain times.If that is the case,I would like to have some type of fix.
I will at some point go back and recheck everything you mentioned although,gut feeling is that something else is happening.
Thanks for the reply.

[maxster]

counter rotation from the lead fan then the other kick in?just for future reference...on the supply fan side and 460 rooftops trane was short on the wires from the contactors to what the motors had so you'll see a line voltage terminal strip looking into the fan belt section at the 2 o'clock positon mounted on the fan shroud.over the years belt dust moisture and fan vibration cause arking on the slip connectors and as soon as you close the fan contactor with the access panel down baa boom you think the motor blew it was the 3 phase terminal jumping on each other remove the sta-kons and wire nut it and wire tie it onto the shroud check the fan contactors thy take the hit also...CFM are rotation in off position

[rgd2005]

counter rotation from the lead fan then the other kick in?
I am going to have a closer look at the counter rotation situation,stickinit2thman mentioned that also.
Thanks for the heads up on the indoor fan.

[Brokanic]

I had that problem before. Almost every week the fuse blow.
Check temp on the fuses using infared thermometer, line side and load side if there is difference in temp change the fuse holder.

[stickinit2thman]

My newly aquired customer has 4 of these package rooftop units,
Mod#TCD600AD0C2BBNF4DH
The 20 amp condenser fan fuses blow from time to time.I first
saw it happen this summer.
The motors ohm out good and draw
about 6 amps.Two (208vac/1 phase) motors per 20 amp fuse
(one 20 amp fuse per line)
I had another call on one of these yesterday where all 4 fuses were blown(all 4 fans offline).Replaced the fuses after checkingfor grounds,open windings and bad run capacitors.Motors came online without a hitch.

Fuses should be time delay or HACR rated to allow for starting of motors.

[stickinit2thman]

Fuses should be time delay or HACR rated to allow for starting of motors.

This may be reaching a bit but is there any kind of weired airflow such as conditions that make downdraft condition and fans are turning rapidly backwards before start-up at certain times and are the units competing for air from other units? Check contactors for proper voltage accross terminals.

[SAILFISH]

Just as an easy way if the customer said the power is dirty install a ICM digitial Phase monitor on the line side of the power inside the unit to see phase problems. I had the same problem and after checking all the above notes in the responce found on leg would drop/brown for a few seconds causing high amp and fuse loss.

[rgd2005]

Brokanic,good point.The fuses have been replaced so may times,
the tension on them may be getting slack.

stickinit2thman,The 20 amp fuses are time delay.I am still waiting on a chance to get back to this job.I am trying to figure
out how to replicate all four fans turning backwards and then
all of them getting powered.The motor repair shop we use has a neat little gadget that can be installed on motor to prevent the backward motion.A little pricey though.

The backwards motion fans is not new to me.I have seen them continue to run backwards when power is applied.

SAILFISH,The units do have the ICM addon phase monitors.It was late the other day when I got the call,but I believe I glanced at it and no faults were indicated.Oh,and welcome to the forums.

[james32]

sounds like the building is having power surges

[JWB]

low voltage, higher amps. fuses blow. brown outs....could it be that simple? data log their voltage?

[rgd2005]

data log their voltage?

Good idea,thanks

[Ansonf]

Since it's happening to all of them, the main thing they have in common is the power source. I those are all good ideas. You could check the electrical room in the building, the breaker for the panel for the hvac? loose main line contact, difference of how much from there to your units?

[rgd2005]

Agreed.I am looking at voltage/power recording options now

[RuralSpaceman]

Found same kinda pblm on McQuay RTU onetime. Eventually learned it only happned during or after rainy weather. Control section was under neg pressure from supply fan and cabinet panels let water draw in and trickle down inside sufficiently to short terminal block on back wall. Of course on a dry day, could not see reason for blown fuses. Made up sheetmetal stand-off for terminal block and later made better panel seals.

[rgd2005]

Thats good to know,thanks for sharing.
btw Welcome to the forums

[Brokanic]

i just had the same problem
installed phase monitor- alarm on under/over voltage almost everyday.
i thought that was causing the fuse to blow almost every two days but i finally spent time on tracing all the wires and found that one wire was rubbing to a point were the intermittent blowing fuse was happening. replaced wire and now the a/c been running fine.

[marvin]

I had that problem before. Almost every week the fuse blow.
Check temp on the fuses using infared thermometer, line side and load side if there is difference in temp change the fuse holder.

i had one almost identical a week or so ago. changed fuse holders &
problem solved. good indicator is the color on each end of fuse.

[Ansonf]

I f you think about it a blown fuse is usually always motor , or wire short.