Original message
| Dog Biscuit
 |  "Contactor Chatter"
, posted Sat 24 Jun 19:10  
This is a 208/3/60 contactor with a 24vac coil on a Lennox 5 ton
furnace/Condensing unit. With an initial 22.6vac available, just as the call for CU to act the voltage drops to 15vac and the contactor chatters and fails to engage. With a manual boost to the contactor it engages and the compressor starts and continues to run. Old contactor did same as the new one just installed. The thermostat is a single stage mercury bulb on cooling. On 3 other identical systems, 22.6 volts works fine.
1.) Should 22.6vac be enough to pull in a 24vac coil?
2.) On a call for cooling, what could cause the voltage to drop
to 15vac.
3.) Are contactors with a 24vac coil used much today?
(Yes, we removed all items between call for cooling and the contactor coil: IE: anti-recycle-timer, high pressure cutout, etc, on the low-voltage circuit.)
To err is human to repair divine
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Replies:
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| weber
| "Re(1):Contactor Chatter" , posted Sun 16 Jul 23:22:
check for 24v right out of the transformer, if you have it there check for it at the stat,(red wire)if you have it jumper your red and your yellow, that should send 24 to the contactor. Check it, if you have it you have to much restitance in the stat, change the stat goto a digital, get away for the merc ones. they sell cheap easy to use digital stats that are simple to use and install. some use batteries and others use a common!
[this message was edited by weber on Thu 30 Oct 21:25] |
| thechiller
| "Re(1):Contactor Chatter" , posted Thu 29 Jun 22:46
Have you checked the transformer, (all 24v transformers are not the same) you should have at least a 40 va (volt/amps)transformer or you can get a volt drop as the different coils energize.
Service you can trust
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| Dog Biscuit
| "Re(1):Contactor Chatter" , posted Sat 24 Jun 23:45
Xenos--- What am I doing wrong to cause triplication of my post.
To err is human to repair divine
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| | Xenos
| "Re(2):Contactor Chatter" , posted Sun 25 Jun 15:30
No idea...
Xenos.
The best way to escape a problem is to solve it.
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| Xenos
| "Re(1):Contactor Chatter" , posted Sat 24 Jun 19:40:
As well as the stat. This could be a bad wire/ connection or a weak transformer.
Xenos.
The best way to escape a problem is to solve it.
[this message was edited by Xenos on Sat 24 Jun 19:42] |
| fitter597
| "Re(1):Contactor Chatter" , posted Sat 24 Jun 19:39
it's the mercury t-stat dropping your voltage i bet.
LOCAL 597 PIPEFITTERS
"We Do It Right The First Time"
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| | SMOKEmadBLUNTS
| "Re(2):Contactor Chatter" , posted Sun 25 Jun 14:14
rooftop?,split? u probably have a shorted control, if its a rooftop look at everything in the cooling circuit like the economizer controls ect.....
Please save the applause till the end
Nate Certified
EPA certified
Specialize in water cooled heat pump buildings
Master Mechanic for a small Commercial/Industrial service only outfit
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| | Dog Biscuit
| "Re(3):Contactor Chatter" , posted Sun 25 Jun 19:11
Feedback and follow-up to my Question:
Your suggestion that the mercury bulb T'stat was questionable prompted us to jumper it---and the control-voltage went from 15vac to 19. Then we placed a jumper in the control panel that isolated both the t'stat and the wires to the t'stat---and the voltage jumped to 26.2vac. Now the contactor is 'slamming-in" the way it should.
Our conclusion is that during a remodel the t'stat wires were compromised. Thank you for the loyal support---DB
To err is human to repair divine
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| | GEOGY KENNY
| "Re(4):Contactor Chatter" , posted Sun 23 Jul 22:51
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| | hvac
| "Re(5):Contactor Chatter" , posted Tue 19 Sep 15:07
I agree with the contactor coil is starting to short out. This would drop your voltage and will blow the control fuse eventually. I have also install a shunt across the coil and it has stopped the chattering before. You can buy them at a electroic store its just a filter.
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| | harpo
| "Re(6):Contactor Chatter" , posted Mon 25 Sep 20:03
always check the rooftop or slit at the rooftop terminal strip as you found,on new units that are being strated up always read the secondary at the TR. manufacturers always tap for the hi voltage when its a 200/208/240 primary go for the 2 lowest even if your reading 210V tap for the 200V and that little more on the secondary!
It ain't going to get any lighter looking at it!
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