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Pbfoot

@sbcglobal.net

Single Pole Contactor replaced, still makes buzzing/rattling


contactors
Last night when my furnace kicked on I could hear a loud rattling all throughout the house. When I took the panels off the inside unit to find the source I found that the single pole contactor was the culprit. Today I bought a replacement part and installed it, but that one is doing the same thing! It's not as loud as before and seems to quiet a little after the heater has run for a few minutes.

Don't pay attention to the text on the image because it's borrowed, but mine looks very much like the picture above.

Any insight from the pros out there as to what would make this keep rattling? The unit is American Standard TWE036C140B0
Thanks!


pike
Premium,MVM
join:2001-02-01
Washington, DC
kudos:3

Any way you could provide audio of the buzzing? That's unusual.

It almost sounds symptomatic of the contactor not fully closing. First make sure the coil is rated for the application. Next, with everything deengerized, operate the contactor with your hand and make sure the movement is smooth and it closes completely with no binding. Also check the voltage at the coil - if some resistance is being introduced somewhere (like a loose connection or bad crimp) it may leave the coil too weak to pull the contactor fully closed.

One other thing I would try, if you are comfortable, is first de-engerize the circuit that the contactor is switching. Then energize the coil circuit. Use an insulated tool or wooden dowel and push on the contactor to see if it closes further with manual intervention.



pbfoot

@sbcglobal.net

thanks for the quick reply. the contactor I bought is the direct replacement for the original. When I press in on the contactor it moves freely. With the furnace off, I press in on the contactor and I could hear the heating coil was getting a connection and was "warming up".
next I'll check all the connections again and test the voltage.
I was wondering- there are two breakers in there, a 30 and 60, could one of these be going bad and cause this contactor to not work properly?


harald

join:2010-10-22
Columbus, OH
kudos:1
reply to Pbfoot

Deja vu, from 47 years ago.

It is probably the limit switch, mounted on the same bracket. Contactor closes, the impact causes the limit switch contacts to open momentarily.

Start by dismounting the contactor. If problem stops, remount it and start dismounting other items, checking for for loose connections, etc.



John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
kudos:6

There are no limit switches on that type of contactor.



nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
Reviews:
·Charter
·voip.ms
·surpasshosting
reply to Pbfoot

3 thoughts:
1) The contactor isn't properly / adequately installed or secured.
2) The transformer is unable to provide adequate voltage / current to hold the contactor closed. *Side question in relation* - Does this furnace have separate sequencers? I'm assuming yes. Is it the last element on?
3) Solid state contactors are available for replacement - they will cost more.

A little more information about the unit would be helpful. I'm unable to find a wiring diagram for the model number listed.
--
If someone refers to herself / himself as a "guru", they probably aren't.



mackey
Premium
join:2007-08-20
kudos:10
reply to Pbfoot

I've had new contactors which were really loud when first put in. After a couple dozen cycles the only noise they make is the "thunk" when switching.

/M



John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
kudos:6
reply to Pbfoot

There might be some dirt between the e-frame and the armature which is stopping the contactor from fully "sealing". This will cause noise. Since the amount of dirt is small, you may not notice it, and it -can- come from the factory like that.

Carefully disassemble it (usually straightforward...release clips on the side) and clean the mating surfaces of the electromagnetic parts. Reassemble and try again.
--
Nothing makes an American want to do something more than telling them they can't.


harald

join:2010-10-22
Columbus, OH
kudos:1
reply to John Galt

said by John Galt:

There are no limit switches on that type of contactor.

Look at the picture. It is adjacent to the contractor, just to the upper left. It may be line voltage, after the contactor, however.

I still bet on a bad "connection" somewhere.


Raphion

join:2000-10-14
Samsara

The confusion here is that harald is talking about the thermal limit switch, and john galt thought he was talking about a mechanical limit switch on the movement of the contactor itself....



Pbfoot

@sbcglobal.net

Click for full size
Contactors

furnace
Click for full size
contactor diagram
Thanks to everyone for the information! Disregard the first picture in the post- as mentioned in the original post that was not my furnace, just a picture that closely matches my contactors.
After installing the replacement contactor, I dismounted it as harald suggested. When the furnace kicked on it continued to buzz as before.
I got out my voltmeter and checked the voltage on each wire with the furnace off and running. As you can see from the first picture, the voltage on the two blue wires are constant when the furnace is on or off, but the white wire is not. As pike mentioned this could be symptomatic of the contactor not fully closing.
Next I traced this white wire out of the box, through two connector blocks, to the group of white wires in picture two. The wire nut did seem loose when I touched it, so I put a new wire nut on it and checked all the others. The problem continues.
The third picture is the wiring diagram that is on the panel covering the contactors. I didn't realize the resolution on the camera was set so low, so if anyone needs a larger picture let me know.
The only thing that I have done recently (last Nov.) was to install a Nest thermostat. No problems installing it and no issues with the furnace until last night.
Again, I appreciate everyone's help. I've been unemployed since last June, so I need to figure this out and avoid calling an HVAC repairman if possible.

harald

join:2010-10-22
Columbus, OH
kudos:1

Disconnect the coil on the single-pole contactor and wire the coil directly to the low-voltage side of the stepdown transformer. (Open the breakers that supply the furnace heating elements first.)

Does it still buzz? I still suspect that there is a loose connection somewhere on the low voltage side.



shdesigns
Powered By Infinite Improbabilty Drive
Premium
join:2000-12-01
Stone Mountain, GA
Reviews:
·Atlantic Nexus
reply to Pbfoot

You measured voltages but to where?

The coild voltages are probably 24V as the schematic shows them as "low voltage side".

What is the voltage across the coil (smaller terminals)?
--
Scott Henion

Embedded Systems Consultant,
SHDesigns home - DIY Welder



Pbfoot

@sbcglobal.net

Scott- I did all the voltage testing on the single pole contactor- I put the black voltmeter pin on the black wire connected to the contactor, then touched the connectors of the other three wires on the contactor.

Harald- I think what you're asking me to do is above my pay grade lol. Is the stepdown transformer part of the breaker? Would that be on the right side of the 60?

I'm by no means an electrician- or played one on TV.


harald

join:2010-10-22
Columbus, OH
kudos:1

Well, have you stayed in a Holiday Inn Express lately?

The issue is, does the contactor chatter with the correct voltage applied to the coil?

To determine this, you need to supply 24 Vac to the coil by what we pros call jury rigging. There is somewhere a transformer that supplies 24 volts to the system. Find the transformer, Identify the secondary (it's supplying the thermostat) and use a couple of pieces of wire to connect it to the contactor. Does the contactor chatter?



Pbfoot

@sbcglobal.net

Well, believe it or not, the symptoms have gone away now. Sunday morning when it first kicked on it buzzed but went away and since then has not done it at all. This was after another round of checking all the wire nuts/connections- I even re-seated the connections on the Nest thermostat. Maybe it was a loose wire somewhere... I don't know.
I'm going to close the book on this little project- THANK YOU to everyone here who took the time out of their day to post recommendations, I really do appreciate it.

Switching gears- I was hoping to get some suggestions for a replacement system down the road (after I'm back to work). What I have now is the American Standard Heritage 12 Heat Pump. Our home is approx 1400-1500 sq. ft., ranch style w/ walkout basement. The lower level is unfinished, but has it's own separate American Standard HVAC system.
Model number on the heat pump is 2A6H2036A1000AB, air handler model is TWE036C140BFB. House was built in 2003.
How can I tell how many "tons" this system is and if it's really adequate for the sq footage. We live in SW MO, so we see both extremes of weather.

Thanks again everyone! The tension spring on our 2 yr old Samsung dishwasher broke last night and about took my shin off! Sigh... off to the next project.



cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7

said by Pbfoot :

Model number on the heat pump is 2A6H2036A1000AB, air handler model is TWE036C140BFB. House was built in 2003.
How can I tell how many "tons" this system is

The 036 indicates the model size, in thousand btus. 12k btus go in 1 ton, so your system is a 3 ton system.

and if it's really adequate for the sq footage.

A Manual J is the best way to determined if it's correctly sized for your location, home usage, and building construction. If the unit can maintain temperature during extreme weather (either hot or cold) and runs nearly continuously, then it's likely sized close to what it needs to be. Oversized, the unit may short cycle resulting in lower comfort and decreased operational efficiency. Undersized, it may not keep up during weather extremes. Sized right, it will run almost not stop during the hottest and coldest weather and only use emergency heat (if equipped) during the absolute coldest weather (other than defrost cycles).


Pbfoot

@sbcglobal.net

I guess it's sized right then- it will run almost constantly during temperature extremes.

If any of you were putting in a new 3-ton heat pump what you go with and why?