Chattering Contactors

[Kphdempsey]

I am working on a chiller system that runs a hydraulic pump as well as a cooling fan. I was sent out to replace the control board for the system as well as a contactor.

I have a transformer running 24VAC to A1 on both the pump contactor and fan contactor as well as a port on my control board. The A2s are tied to separate ports on the control board.

Long story short. One of the brand new contactors is clicking off and on. (Apparently had been before I got called). I have measured the coil voltage for both contacts. The one that is working correctly is a constant 24V. The other runs fine and when it clicks, the voltage jumps up to 28V. I am unsure of what to check to remedy this. For me, it seems that the voltages should be the exact same across the coils.

 

[Pete999]

I am working on a chiller system that runs a hydraulic pump as well as a cooling fan. I was sent out to replace the control board for the system as well as a contactor.

I have a transformer running 24VAC to A1 on both the pump contactor and fan contactor as well as a port on my control board. The A2s are tied to separate ports on the control board.

Long story short. One of the brand new contactors is clicking off and on. (Apparently had been before I got called). I have measured the coil voltage for both contacts. The one that is working correctly is a constant 24V. The other runs fine and when it clicks, the voltage jumps up to 28V. I am unsure of what to check to remedy this. For me, it seems that the voltages should be the exact same across the coils.

Poor electrical connections, dirty magnetic pole faces, not been wired in series have they?

 

[Kphdempsey]

Poor electrical connections, dirty magnetic pole faces, not been wired in series have they?

I'm going back out there thursday. I am starting with the connections in other places. (The contactors are brand new). Not in series. The panel builder made some very odd choices, so a tech has to completely unwire most of the system due to daisy chaining just to see where things are actually connected.

 

[marconi]

Could you temporarily connect 24AC directly from the transformer to the clicking contactor's A1 and A2 (having first disconnected it of course from the control board) to see if it clicks? Remember to isolate the input power (or output power) to(from) the contacts of both contactors so that you do not energise the motors they control.

Then, temporarily connect the A1 and A2 of the other contactor in parallel with it.

This will provide some information on the satisfactory operation of the contactors themselves.

 

[Kidsolo]

I would be looking on the control board.

 

[Kphdempsey]

Could you temporarily connect 24AC directly from the transformer to the clicking contactor's A1 and A2 (having first disconnected it of course from the control board) to see if it clicks? Remember to isolate the input power (or output power) to(from) the contacts of both contactors so that you do not energise the motors they control.

Then, temporarily connect the A1 and A2 of the other contactor in parallel with it.

When I was there it was hard wired, but I am definitely going to try that when I get back. Thank you

 

[Pete999]

Be good to know what the problem is ,thanks.

 

[Lucien Nunes]

If the voltage reading on your meter is only rising briefly to 28V when pulsed, that may just be back-EMF from the contactor coil and not indicative of incorrect voltages. It sounds like the control board is switching the contactor on and off, and whatever was making the old board do it, is making the new board do it as well. So both the old board and contactor may have been OK. I would connect a small auto lamp or max/min reading meter across the coil to monitor the board output. If it is pulsing in time with the contactor, then the search can move on to what is causing the board to do that.

 

[Megawatt]

I am working on a chiller system that runs a hydraulic pump as well as a cooling fan. I was sent out to replace the control board for the system as well as a contactor.

I have a transformer running 24VAC to A1 on both the pump contactor and fan contactor as well as a port on my control board. The A2s are tied to separate ports on the control board.

Long story short. One of the brand new contactors is clicking off and on. (Apparently had been before I got called). I have measured the coil voltage for both contacts. The one that is working correctly is a constant 24V. The other runs fine and when it clicks, the voltage jumps up to 28V. I am unsure of what to check to remedy this. For me, it seems that the voltages should be the exact same across the coils.

Try going back Through the whole control circuit. Is the output on the control board pulling in both motor contractors or do they have separate outputs ?

 

[R-fur]

I Agree with Lucien above. Is this a DC system? if so the contactor coil should have a snubbing diode or resistor across it to kill the back EMF when the coil is de-energised.
Without a snubber the back EMF could be causing the control contacts to arc and burn. This burning could cause the contact to make a bad connection so the coil chatters in and out and causing more arcing and so it goes on. Then someone replaces the contactor but it still chatters because of the burnt control contact.
Just a thought.

 

[Megawatt]

I Agree with Lucien above. Is this a DC system? if so the contactor coil should have a snubbing diode or resistor across it to kill the back EMF when the coil is de-energised.
Without a snubber the back EMF could be causing the control contacts to arc and burn. This burning could cause the contact to make a bad connection so the coil chatters in and out and causing more arcing and so it goes on. Then someone replaces the contactor but it still chatters because of the burnt control contact.
Just a thought.

What little bit I know is the control voltage is 24vdc

 

[marconi]

ac - see #1