We bought a condo and had a fire. The ac company shorted out the wires on the roof of this 10 story building and the thermostat exploded and there was quite a fire I extinguished. All was made whole by the insurance company. The vents were cleaned and thermostat replaced along with with cleaning and restructuring the wall.

My question is that we just started using ac because it just started warming up and there is a pinging metallic noise when the air is on. The ac person has removed the blower motor and checked all he can but the noise is enough to keep you awake.
To our knowledge the inspector did not hear any noise before we bought it and neither did we.

The tech is thinking of enlarging the taped trunk space so there is less volume of air as it is really powerful. He is hoping this will stop the noise.

Does anyone in ac have any suggestions as to how we can stop this noise?
Is a camera in the duct reasonable?
Thank you

 

Quite a fire from a thermostat


A pinging noise is usually caused by a loose damper in the ductwork. I'd check that first.
Noises are extremely hard to diagnose online. A camera inside the duct might help.

 

I'll pass that along to my tech.
Is there a fix besides cutting into the duct. It is part of the bedroom and painted to blend in.

 

The first step is to locate the source of the sound, which we can't help with. Many dampers can be adjusted from the outside so there might not be a need to cut into the duct but first you have to determine if that's the source of the sound.

Where is your air handler located? Does it seem like the sound might be coming from it. I have seen one where condensation was dripping onto the fan and made an annoying "ting" sound every time a drop hit the spinning, sheet metal blade.

How is your condo heated? Is it forced air and use the same ducting as the AC? If so do you hear the noise when running the heat?

 

I will ask about the air handler.
It is heated and cooled the same ducts. It is a heat pump.
I tried to send some photos for you to get an idea but it failed. The unit is in the closet of a condo but being in a 10 story building which just had a new roof built, there is some "stuff" on the roof. That is when the fire started. He went on the roof and said we would have heat in 10 seconds then the thermostat blew up. He said there was old wiring in Leisure World and copper shorted out.
After the fire we started to hear this noise but it could have n been there before, the inspector did not hear it either.

 

I hope this shows the closet with the heat pump in 3 views and the noisiest vent in the bedroom; they are all noisy.

 

Well, if the same unit heats and cools and you did not have the noise when it was in heating mode that's a clue. Have you tried to locate the source of the sound? It should be easy to tell if it's right near a register or somewhere else.

 

The noise is between the heat pump and the first vent.

 

In the picture I modified.... what is the thing I circled ? Is that a hole ?
It looks like it may have been for a damper. I couldn't quite figure if the orientation of the picture is correct.

 

The word "ping" is not very descriptive. Is it a single noise when the fan/blower first starts and it is then quiet, does it make a noise when the fan stops? Or is it a repeating noise? If repeating, then what is the time cycle between pings?

Since the fan/blower almost always runs significantly faster in cooling mode than in heating mode it is possible that the ductwork bracing is borderline and it is the duct flexing under the higher pressure that causes the noise. If it were a whistle then I would vote for restricted ducts or grilles.

 

The noise is not easy to "say" - it is a metallic noise, and a mixture of metallic sounds like pings as if if you flicked a tin can top when open with your fingernail.
It is tinny for the most part.

If we are not mistaken, it does not occur when heat is on, only ac.

The tech said he is going to enlarge the trunk so there is less force which seems to go along with your thinking about duct bracing and speed of air.

I am keeping all these notes for him to read when it is hot and he comes over again.

**post number 8 is not correct as it runs to all vents

 

Dunno - maybe not applicable in a tall building, but I had a pinging noise in my heat pump right outside my bedroom wall, drove me nuts. Tech said was leftover rainwater dripping from the top grill down onto the fan (frequent rains that summer). Sure enough, when the outdoors dried up the pinging stopped, so it really never worried me when it happened again.

 

Thanks but this occurs when it is dry.

I guess a good question is, " Do most heat pumps with ducts make noise or is it an exception?"

 

No, most heat pumps or any other type don't normally make an annoying pinging noise. If your coil is located above the fan I would I would see if condensation is dripping down on the fan.

 

Does your thermostat have a fan auto/on switch? If yes, then try moving it to the on position and see if the noise occurs. The on position generally runs the fan at the cooling speed and this should tell you if it is an airflow problem or something specific to the cooling cycle. Obviously you have to turn the thermostat temperature setting high enough that the cooling is not energized or else just switch to the heating mode temporarily.

 

Thank you both for replying.
I think we better get used to a lemon.

 

To answer your question, I did turn the fan on manual and there was no noise.

When the unit is on ac does it blow as hard as when the fan is just on manual?

From what has been discussed is there any indication it is the compressor?

Could the electrical short that caused the thermostat to melt and the fire to start have damaged the unit. The tech says no because there is a fuse that would have blown first.

 

Yes, it is a hole in the duct that runs into the kitchen -nothing inside except insulation.

 

Usually. It does depend upon if you have a variable speed blower motor or if it is the standard three/four speed motor. When you use the fan switch in manual is it a high speed and forceful air flow out the registers or a barely perceptible very quiet flow? If the latter then you have a variable speed unit and the test is meaningless.

I think you should put some tape over that hole in the duct. Foil duct tape is best but anything will be better than the hole.


I don't. The noise is something wrong and it CAN be fixed. The problem is finding out what causes the noise and then working it directly. That it ONLY happens when in cooling mode is important.

That "stuff" on the roof...do you have any access to it? Maybe get someone from maintenance to give you access and then take a picture. I suspect what is there is the "condenser" unit and this is where the compressor would be located. There would also be two copper tubes running from the condenser to the air handler in your closet. It might be something as simple as the copper tubes rattling against themselves or the ductwork. The tubes are supposed to be insulated but it is possible the insulation is missing somewhere.

One more question...does the pinging start immediately upon the thermostat engaging or does it take a few minutes?

 

Thank you for the encouraging words.
I will pursue this thread with the tech.
He said no cost to us so the building must be assuming fault.
The noise comes and goes.
Usually it makes the noise after the ac is on for a little while but it is really fickle.
As you can tell this is really an up on the air situation.
I will keep you updated when the tech returns.

 

Compressors often have a delay timer and so do thermostats. This means that if you have both, it could actually be as long as ten minutes before the compressor starts in some instances. During normal operation the compressor will often cycle off and on during more moderate temperatures.

Definitely sounds like it is compressor related and also quite possible it is the copper piping that is vibrating under certain circumstances. The biggest problem is that it is intermittent and following a corollary to Murphey's Law, it will rarely make noise while the technician is there to hear it.

 

Thanks for all the information.
I will have the tech read this thread when he comes over. The compressor is not covered as far as I know and it is expensive. Just what we needed.

 

I had a similar situation after both the heating and ac units were replaced in my home, last fall. As one who replied said, " if you didn't have the noise before, then that should give you a clue." Something that was replaced is expanding (or contracting- probably at a joint where the sheet metal was folded to seal it) or contracting and giving you the tic'ing or pinging sound. That's my uneducated guess. I'm not a HVAC tech. But, I will tell you that my unit, over time, seemed to have lost its annoying sound when the unit runs. Good luck.

 

Thanks for the advice -maybe we will be so lucky.