Carrier rtu, breaker tripping every 2-3 days

[fishunterhvac]

hi everyone,
got question on carrier 48TFD009-511BA S/N:1802G50521
y1 & y2 jump at the terminal block at the unit,unit will come on for 1-2 seconds and shut and for about 2-3 second then will come on again and run ok .check electrical connection,amp draw of both comp., and both cond. fan,breaker size,pressure ok.now this unit run like this for 5 yrs,should i put a time delay on the y2 terminal or should i replace the stat with a 2 stage cooling,will this fix the problem? should i replace the breaker(maybe the breaker is getting weak)cond. fan check ok,cond fan mfd ok.coil & filter ok.
thanks in advance
fishunter

[mikelcs]

a two stage unit needs a two stage stat. when the stages are coming on together, do they both shut down then restart, or only one of them? use your meter and see where you are dropping out. if both compressors are dropping out and restarting together, my guess would be that there is a problem with the stat.

[fishunterhvac]

everything shut off then start again.

[mikelcs]

everything including the blower?

[berg2666]

My guess the condensor coils are dirty and it is causing the condensor motors to heat up and overamp causing thebreaker to trip. and your compressors are overamping also because of the dirty coils. Take the NUBRITE to the condensor coils before you replace the breaker....

The high side pressure is no high at start up but increses as the unit runs...

[fishunterhvac]

yes including the blower,total amps on start up is 25.6,has a x3 45amp fuse at the disconnect none of them ever blown,OT 78, IT 75, pressure 64/226.
cond. mtr both pulling 1.0 rated at 1.4.i watch this unit for about 45 minutes yesterday and today for 30 minutes and check my amp reading 5 minutes before i headed home and still reading ok.now on the same roof theres another unit that is doing the same thing but is a single stage(smaller unit)but not tripping the breaker,now on the west side theres exact same unit 2 stage cooling but run just fine with y1 &y2 jump at the unit.as i mention earlier i was here today so i installed a 2 stage cooling stat and did not make any difference at all.cond. coil was cleaned 2 months ago.

[y7turbo]

Did you check the contactors?

I had one doing the same thing as what your talking about and that was the problem. It was pitted and discolored very badly. it would start fine then the contact would heat up after a while to the point where the connection started to get lost and trip the breaker. That damn thing tripped about 3 times in the hour I was there, after the contactor it never did it again.

[lirunaway]

Did you check the contactors?

I had one doing the same thing as what your talking about and that was the problem. It was pitted and discolored very badly. it would start fine then the contact would heat up after a while to the point where the connection started to get lost and trip the breaker. That damn thing tripped about 3 times in the hour I was there, after the contactor it never did it again.

Therefore your other units will eventually do the same thing because with Y1 & Y2 wired together your cycling both compressor contactors more frequently than design.

[fishunterhvac]

Therefore your other units will eventually do the same thing because with Y1 & Y2 wired together your cycling both compressor contactors more frequently than design.

well contactor seems to be fine,theres three of them one for the blower and two for the comp. will they go bad at the same time?

[crawdad55]

Try checking the transformer primary AND secondary. What is th VA rating on the transformer. It could be getting weak. It has enough voltage to pull in one contactor but can't hold two.

[GOVHVAC]

Have you looked for a bare wire? I had this problem on a Trane RTU, four techs had looked at it and couldn't figure out why it was tripping the breaker intermitently. I found a bare spot on the line voltage wire coming into the unit. The insulation was rubbed off and touching the metal, it would vibrate while the unit was running then everyonce in a while it would touch the metal. So the techs would reset it and it would run for a while then touch and trip the breaker.

[james mo]

May be a low voltage issue. Digital thermostat flaking out, voltage drop of the secondary due to a thermostat, long t-stat wire run, improperly tapped transformer. What is the voltage of the secondary and what does it drop to when you energize the unit?

[keepyoucool2003]

Sounds like the customer should call someone that knows how to troubleshoot commercial equipment. You have to think in and orderly way of what could be causing the problem and work back.

[fishunterhvac]

i know is not the tstat cause i jump R,Y,G at the unit,no bare wire found that will cause the problem,
We found loose connection at the breaker,tight the loose connection and it works just fine, but we change the breaker anyway.

this casino has over 300 unit 68-25ton carrier rtu on the main casino,200 mini split(fujitsu) on every suite,30+ 5 ton carrier Split heatpump for conference rooms,10-10-12 tons carrier rtu.this company installed all this unit 2 years ago.and we have a contract with them,so they cant call another HVAC co. that has a tech that know everything about commercial ac.there stuck with us for 1 year.so being a green horn tech. i come to this Forum to ask question(everybody start somewhere right?)i might not know everything about hvac resi/comm but i do apply what i know.i know a lot of tech that has 5-15 yrs experience and cut so many corners,dont recover,vacuum,bypass safety control etc.i dont do that. i take pride on my work,i like to do the right thing,i just wish i could ask question here without other people making me damm,believe me i already know.i come to this Forum to learn not to get critisize.

[chillersandcontrols]

fishunterhvac:

Good for you! Give those critics the unicorn salute! LOL!!!

Man, the ONLY stupid question is the one you DON'T ask.

Assume Nothing! Question Everything!

Just a Suggestion: Get yourself a small Infared Thermometer like Fluke, etc. I have found many a hot spot on contactors, coils, solenoids and especially in breaker panels - cause they never get checked until something BLOWS. Just point that laser dot around the control panel and find the loose connections!

Get your Carrier distributor to set you up with literature on all that Casino equipment. Carrier does some wierd stuff in their new equipment so read carefully!
I strongly recommend thermostats to match the RTUs, i.e. 2-Stage stat on a 2-Stage unit. Some Carrier units require very specific thermostats due to electronics in the unit, so read the IOMs carefully.

Have Fun!

[fishunterhvac]

fishunterhvac:

Good for you! Give those critics the unicorn salute! LOL!!!

Man, the ONLY stupid question is the one you DON'T ask.

Assume Nothing! Question Everything!

Just a Suggestion: Get yourself a small Infared Thermometer like Fluke, etc. I have found many a hot spot on contactors, coils, solenoids and especially in breaker panels - cause they never get checked until something BLOWS. Just point that laser dot around the control panel and find the loose connections!

Get your Carrier distributor to set you up with literature on all that Casino equipment. Carrier does some wierd stuff in their new equipment so read carefully!
I strongly recommend thermostats to match the RTUs, i.e. 2-Stage stat on a 2-Stage unit. Some Carrier units require very specific thermostats due to electronics in the unit, so read the IOMs carefully.

Have Fun!

thanks! i have a raytek ,next time i'll do that.

[maxster]

check that secondary on the 24V TR make sure your tapped for the actual voltage on the primary...208V tapped at 240V will give you a low secondary and cause the contactors to drop out and pull in as other fans come on and pull on that 19V-21V????.if the units are a typical check the TD on another of the same style with that jump at the Y1-Y2 then go to the R to see a 2nd stage TD within the rooftop from Carrier.TDs relays can shorten up or just disapppear when failing causing 2 compressor loads to pull thru that breaker, heat up the metals within and trip on another start.make sure the circuits are inline with the other units staging......standing in front of the compressor compartment which compressor starts as the first stage.

[The Doctor]

check that secondary on the 24V TR make sure your tapped for the actual voltage on the primary...208V tapped at 240V will give you a low secondary and cause the contactors to drop out and pull in as other fans come on and pull on that 19V-21V????.if the units are a typical check the TD on another of the same style with that jump at the Y1-Y2 then go to the R to see a 2nd stage TD within the rooftop from Carrier.TDs relays can shorten up or just disapppear when failing causing 2 compressor loads to pull thru that breaker, heat up the metals within and trip on another start.make sure the circuits are inline with the other units staging......standing in front of the compressor compartment which compressor starts as the first stage.

I second the motion for a xfmr drain on startup due to improper staging. Sell that guy a 2-stage stat, for the love of Pete...:p

There was a Carrier once upon a time ...well okay Friday morning that I PM'd and turned on the ABB on/off switch and nothing happened. Normally it brings on blower almost immediately. Turned it off and then back on and it ran. ....hmmm....better look at this a bit more closely. Have had a few of those ABB(gray and red) on/off switches do funky things to me this year, so... Turns out one load side leg on the ABB was burnt-up and/or the lug was loose. Fun with raw sheet metal edges and stripping back, then everything was everything once again.
There was a large fused disconnect on the top corner of the unit, AND a factory-installed ABB on/off switch (aren't there usually only a need for one or the other?)

Hope that you can sell that customer on your solution...I wish you success.

[maxster]

SF*HC styles ever try to get a second or third start by using the unit mounted CBs for the supply fan... toooo hot from the lock rotor amps draw have to let it cool down..if the compressors and CFs are all coming up the breaker will never hold it

[chillersandcontrols]

Check out the notes on the wiring diagram, Figure 55!

http://www.box.net/shared/xk3iatezvx

[union boy]

hey don't listen to the other guys, we all need help some time.
I would look for voltage drop on startup low voltage and line voltage.
I'll bet the breaker tripps due to short cycling of compressors.
now lets figure why it shorts cycles.
look for voltage drop due to dragging contactor. (low voltage)
long control voltage runs.
low-high pressure switch leads shorting on refrigeration lines?
Gregg

[maxster]

if there semi compressors check in side the terminal box to see that the eyelet connectors are tight with those slotted lock downs they use that lock the eyelets onto the terminals...if their loose that will go right back to the CB on a start...might want to just meg the compressors from the bottom of the contactors to ground to see whats going on with the windings.another trick at the contactors with all the power off(disconnect down)..put your OHM meter top (L) and bottom (T) of each leg and cycle that with a manual push in to see continuity or do an audiable check all legs and if it is 460volts make sure the covers are on the contactor....on a start i have have seen arching trip breakers

[cjcargo]

I had a issue simular to this with a Trane. The pressures, tempertures, voltages and connections all good. Thought maybe a week breaker. Was tripping stage two breaker. This was going on only durning cooler nights. All the low ambient equipment and controls worked fine.
The system was plenium return and had a restricted screen. Had to climb above the supply ducts to find it. Removed and no problems since.

[carriertechny]

how manny cond fans?make sure if motors have been replaced that they where replaced with the right motors .check unit tag not just the motor tag.

[sroberts]

ARE YOU TALKING ABOUT THE BREAKER IN THE UNIT THAT JUST THE COMPRESSORE ARE ON?

IF SO : IS THE UNIT WITH SEMI- HERMTICS COMPRESSORS? i HAD SIMILAR PROMBLEMS FOUND THAT ON SEMI'S THE ELECTRICAL CONNECTOR INSIDE THE COMPRESSORS WERE BAD, AFTER I REPLACED NO MORE TRIPS.
GOOD LUCK ,DON'T GIVE UP

[madhat]

Carrier likes to Daisy Chain their control wiring. I'd look for a broken solderless terminal, or a break in the wire where it goes into a terminal, on the common side. Had a unit that did the same thing, then I got a night call, and could see the arcing at night. Arced when the unit first started from the vibration at start-up. Almost drove me crazy trying to figure out what was going on in the bright sunlight.

[mikelcs]

ARE YOU TALKING ABOUT THE BREAKER IN THE UNIT THAT JUST THE COMPRESSORE ARE ON?

IF SO : IS THE UNIT WITH SEMI- HERMTICS COMPRESSORS? i HAD SIMILAR PROMBLEMS FOUND THAT ON SEMI'S THE ELECTRICAL CONNECTOR INSIDE THE COMPRESSORS WERE BAD, AFTER I REPLACED NO MORE TRIPS.
GOOD LUCK ,DON'T GIVE UP

I agree- meg the compressor- if it fails, remove the terminal plate and meg directly on the motor leads. This will tell you if you have a failed motor, or terminal insulators.