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I am working on a york air cooled screw chiller. Both

Customer Question
circuits trip on overcurrent when...
I am working on a york air cooled screw chiller. Both circuits trip on overcurrent when starting shortly after attempting to start up. I replaced the contactors about a year ago because they were heavily damaged from arcing. I've checked the new ones for damage and there is already considerable arcing which I cleaned with a file and emery cloth.
What else would cause both compressors to trip on the same fault?
Submitted: 2 years ago.Category: HVAC
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Answered in 1 hour by:
2/24/2016
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 2 years ago
Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
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Satisfied Customers: 1,000
Experience: I have been an HVAC/R mechanic/technician for 30+ years.
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Hi I'm Brian and I'm here to help!

I believe if you look closely at the wiring diagram that the mechanical high pressure switches (not pressure transducers) are in series with the motor overload circuit. I would check for problems with the condenser fans or condenser coils. I'll see if I can find my manual for these models and try to confirm my suspicion but I've experienced this same issue on a few York chillers and it wasn't the motor or motor control at all, it was the high pressure cut out peanut relays.

-Brian

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HVAC Technician: Brian HVAC Guy, HVAC Technician replied 2 years ago

Click Here for a copy of the York IOM manual for the chiller in question. In detail A on page 76 you can see what I was talking about with the high pressure switch being in series with the motor overload circuit M1-M2. Check the condenser fan starters or contactors, check the condenser fans themselves and check the condenser coils for fouling. I believe you will find your problem there.

Let me know if you have further questions on this subject. Otherwise, please remember to rate before leaving (3 stars or higher please!). Bonuses are always appreciated! Thanks for allowing me to help and thanks for using Just Answer!

Thank you,
Brian

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Customer reply replied 2 years ago
I see where you are going with that, and I had the same thought. However, the compressors only run for about 30 seconds before shutting down. While watching the display on the controller, It seems like they are starting under load. The inrush current doesn't go down quick enough before the controller shuts them down on overcurrent. It was cool outside when I was troubleshooting like 45 degrees. The water in the evaporator wasn't overly warm, maybe 75 degrees. I can't see why the compressors aren't getting up to speed so the running current falls within the tolerable range. They are at around 110% of full load.
HVAC Technician: Brian HVAC Guy, HVAC Technician replied 2 years ago

That sounds pretty odd indeed. Can you give me the FULL model number of the unit please? Do you know if the unit is Xline start or Wye-Delta start? If it's Wye-Delta, are the starters transitioning properly? I would also check the load/unload solenoids. You can dry run them with jumpers. I've not got a whole lot of experience on the smaller York semi-hermetic screw compressors but at 30 seconds after start, they should just be starting to load so that is rather odd unless the unload solenoid isn't working or the slide valve isn't operating. Are you saying both compressors are doing the exact same thing? That in itself doesn't lend itself to a solenoid or slide valve issue. If both compressors are behaving the same way, I would look for some kind of electric commonality. I would test run everything that can be with jumpers at the control output relays (with the exception of the compressors) to see that everything operates properly from the control panel. Have you double checked voltage, amp draw and system pressures to make sure they jibe with the control panel readings? If you can get me the model number info and answer as many questions I've asked above, I may be able to get a clearer picture of things. As I'm sure you can imagine, it's tough to troubleshoot a chiller this complicated remotely but I'll do my best!

-Brian

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