I live in a townhouse. I have neighbors on either side, but nobody above or below me. The units all have flat roofs. I have an AC unit on my roof. When the AC is running, inside my unit, you can hear a weird, throbbing, kind of vibrating noise. My neighbor has also complained about it.
I had an AC guy out today. He said the unit was only a couple of years old and is running fine. We went on the roof, and it was quiet when it was running. He also said the unit was mounted properly (on cork? I think), and there was really nothing he could do. He said I could try moving the unit to another location on the roof, but that would cost $1500-$2000 and might not solve the problem.
So, I thought I’d check here. I can live with the noise, but my neighbor is a complainer. Has anyone run across this kind of thing before? Thanks.
So you went on the roof while it was running and it wasn’t making any noise…could you hear it from inside though?
You need to wait until it’s making it’s “weird throbbing kind of vibrating noise” and then run up to the roof and see what’s going it. I have some guesses, but it’ll probably be clear what it is when you take a look. Most likely either then entire unit or the fan motor will be wobbling and you can go from there to rectify the situation. Could be a bad fan blade, bad motor mount, bad compressor mount, or a few other things, but I’m guessing you’ll be able to tell. Of course it may just be resonating with the archtechture of the building in which case it may be a bit harder to deal with.
JoeyP, yes the AC was making the noise inside. It always makes the noise inside when it is running.
The AC repairman who examined it said it was running properly and that nothing needed to be fixed.
Chefguy, what are vibration isolators? It looked like it was mounted on two pieces of wood to me with some cork between the wood and the unit. The AC repairman mentioned that I could try spring mounts. Is that the same thing? He didn’t think they would help, though.
Hmmm, if it was making the weird noise inside, but was quiet when you went and listened to it, I’m going to guess it was resonating with the building. That is to say, that it was vibrating just right that it was causing the building to vibrate, and that it’s the building causing the noise.
Possible fixes…
Trying putting something heavy on it, perhaps putting some bricks on the unit itseff or on the wood if possible. This may dampen the vibration a bit, or at least change the vibration pattern enough that it won’t resonate any more
After that the suggestion get a little more difficult/arcane.
You could try moving the unit, even a few inches might make a difference
You could try adding some spring/rubber mounts under it. Again this would help change the speed it which it vibrates and get it to stop resonating.
Is there an attic under this unit. I almost wonder it adding some wood between the trusses would be enough to stop the resonation.
Basically if it is what I think it is, it’s that the AC unit and the building like to vibrate at the same speed. If you can chang the speed of one of them, it may stop.