Trane unit makes constant buzzing/vibrating noise

[jsheld]

Here's the issue - I have two Trane units. The uppermost Trane unit (in the house itself) feeds the upstairs to the house (there are two units in the attic). I'm not sure of the model number - the manual is next to the unit in the house but it has several model numbers listed; the manual is marked with 18-CD1904-5 if that means anything. Anyway, long story short - I walk in the hallway upstairs and hear this buzzing noise when the unit is not running (it is turned off). I go into the attic to the unit and pull off the top part. I can hear the noise but have no clue as to what it is. When I remove the bottom unit, the buzzing stops. With the removal of the bottom unit, I see the control circuit board and a black button. When the bottom part of the unit is placed back on, it hits the black button (pushes it down), and the buzzing starts.

I believe this issue has been going on for a while. I removed the bottom part of the unit again and pushed the black button down with my finger, which once again causes the buzzing noise. The control board is fine - I get cold air and heat (tested thoroughly) and the DS1 light flickers on and off when the black button is pressed down (I believe this is simply a diagnostic indicator for the control board as I see the same thing on the second unit in the attic when the same procedure is followed). Additionally, what's worth noting is that I do not hear the buzzing when the air or heat are running. The same applies when I have the fan on (no buzzing noise).

After doing a lot of research (as much as possible), the only thought I am left with is that perhaps the relay needs to be replaced. I'm not sure if that's the case. Again, I don't believe it's the control board because I am getting air and heat when the thermostat is adjusted. If anyone has any ideas, please let me know.

Email me for the link to the video... For some reason, I can't post the link here and this site won't let me post a wmv file (ugh!). Thanks!

[buzz]

its probably a 110/24 step down transformer thats making the noise,it's either in the relay or on it's own near the control board

[OTM Doc]

The reason it stops when you pull the lower cover off is the safety interlock is made by the cover. Take the cover off and then push in the cover switch, see where the hum is originating. Remember, 120VAC is present so use a care.

[jsheld]

That's the thing... it appears that the sound is coming from the left of the circuit board. I believe the piece there is the relay, if I'm not mistaken. I was going to upload a photo, but the photo I have is too large for the site . The part number is C340041P01 - from what I can tell, I believe that is the transformer. The sound has been going on for a while now - is that ominous or what?

[HayZee518]

transformers make a little noise but nothing as obnoxious as you state. they're made up of iron metal punchings with copper wire wound around them. those laminations are supposed to be laid one on top of the other with a sort of insulation coating between them. if this stuff leaks out then the laminations start vibrating. current is changing polarity 120 times a second causing the vibrating. IF a fan relay or contactor is installed the contactor being larger and also uses a laminated construction within the coil and contact crossbar. dirt in the magnetic gap will make the thing vibrate badly.

[jsheld]

So are you saying that the transformer needs to be replaced, or it can be cleaned? From the photo I have, it doesn't look like you can do much of anything to it other than replace the part.

[HayZee518]

no, transformer can't be cleaned. if you are sure the buzzing is coming from it replace it. but I would look a little closer. if there is a motor contactor I'd check that out. a small relay like ones encased in plastic sometimes do hum but not loudly. allis chalmers, arrow-hart make a fan contactor that may hum.