Very loud ac noise (Merged Multiple Posts Into One Thread)


Old 08-04-13, 06:03 PM
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Very loud ac noise (Merged Multiple Posts Into One Thread)

Hello all!

Couple months ago we started having some ac issues. Our unit as a rooftop Ruud about 13 years old. Never really had any issues with it, but couple years ago it started blowing hot air in the middle of July, here in Phoenix. Our ac guy came to fix it with whatever parts he had, instead of replacing bad capacitor with OEM one which he didn't have, he home made something with two smaller amperage capacitors. We never really noticed the difference in any way, nor our bill so we just let it be. We do have Rheem dual capacitor on hand, which is OEM replacement for our unit, but never got to replace it as of yet...
The problems we got have to do with loud whistling noise coming from the vents inside the house. All of a sudden it got really loud, and we can tell it is not operating normally. Two weeks ago, whistling sound got accompanied by a low rumble while ac is on, and our entire house vibrates. When ac shuts off after a cooling cycle, you can hear faint squeaking noise from the vents, for about 10 seconds, almost like fan blades turning to a stop, but this is really faint...
Other than the noise, ac is still cooling properly, although i dread this month bill, which will tell us if it got impacted by the problem or not. MY husband was on the roof today, and he didn't find anything really weird, other than a small crack in the duct which was leaking cold air. He sealed the crack, but of course, that didn't help. He also noticed that the entire portion of the duct which sits on the roof is vibrating on the sides when ac comes on, and he said that there might be a blade on a fan that is a bit bent.
We really need help with this, I can't afford technician right now, and parts are not that expensive, so we would like to see if this is a problem we can solve on our own.. This problem actually started happening after we had a guy do a tune up on our ac, but all he was interested in was selling us a brand new unit.Thanks in advance!

I turned the fan on, and ac, in fact, operates completely normal, no noise, no rumbling no shaking. So it's only when it actually cools and the fan is on auto that we have vibrations thru the house.
My husband tried to rotate fan with a stick today with unit off, and the fan made quite a few free rotations before it stopped. There was no grinding or any noise from the fan with unit off.
When i turned the ac on, he said that fan still didn't make any noises on the roof, but entire ac and the duct were both vibrating. It feels like a low thunder inside the house, with a whistling noise coming thru the vents, and that whistling noise goes up and down in volume constantly as ac cools. We are lost for words. I have aguy coming in the morning to check it out in the morning, but repairs will have to be done by us, due to financial restraints. I just hope it's nothing too expensive

Thank you for all your help! We just had HVAC guy over, and i am actually surprised by his conduct, which sometimes isn't the best here in Phoenix. He actually took the video of our problem, and the problem is a bent fan motor shaft, which, in turn, causes fan blades to spin erratically and on of the blades is touching the sides inside the ac unit, which is responsible for the thunder-like sound.
Even on his phone, you could clearly see the vibration of the fan and the motor. Now, i am not sure what kind of force causes motor shaft to get bent like that, but since that is the problem, we have to deal with it. He was unable to find the part from his dealer, which is okay since i probably can't afford their prices for repair.
Is there a temporary fix for this? Or should we look for motor alone, or whole assembly with the fan, which might be complicated to find? What are our option right now?
In any case i hope it can go for couple more weeks at least, with the noise and all..

I ordered both today, but it will take few days before we receive it Hopefully it will keep working, loud as it is.

So now that we know what is causing the extreme vibrations from our ac unit, i was wondering how difficult it is to replace these parts. We have rooftop Ruud unit, and HVAC guy said that fan motor shaft is bent, and one fan blade is extremely damaged, which is causing our entire house to shake and rumble when ac comes on. I managed to find both parts brand new and at a great price, but my husband is not good with electricity and wires, in fact, few years ago he attempted to switch out or built in oven and oven went to waste in about 2 minutes,so we had to buy a new one and call professional. There is this pattern that keeps repeating itself throughout our 1974 home, everything we buy either has an extra wire, or one less, so he is never sure how to properly connect wires without smoking stuff out to death.
We watched few you tube video, but most units are commercial ones,and those repair guys make things sound super easy. Sometimes wires are colored differently on the old part and the new one, so how do you know which wire is which? I know i might sound pretty stupid, but there is no way we can afford to call someone, we have no credit cards, no saving and no family here, so we can either do this on our own or not at all
What's the best way to approach the wiring, so we don't burn the unit down?


If you are thinking of the dual capacitor, with 3 prongs on the top, we have that new too, but i am not sure if it's a such a good idea to touch that. Couple years ago our capacitor died in the middle of Arizona summer, we called the technician and instead of having it replaced with oem part, he homemade capacitor from two different ones. So far we had two HVAC techs telling us about those, they recommended changing it to the correct amperage dual capacitor, but other than that they agreed that for now "it still works".
I am thinking that wiring was also altered in an effort to make our ac work back then, so i doubt that capacitor would be simple switch from old to new? Maybe i am wrong, but i can have my husband at least visually observe and take pictures.

To our disappointment, it turns out our problem has nothing to do with fan motor and faulty blade (blades are just fine), it was the furnace blower that we needed all along. HVAC guy quoted us 750 bucks for the part and labor, which we can't afford. Now i have to return parts i bought, wait for credit and buy furnace blower.

I have three questions:
Does furnace blower comes with blower wheel? He has that on his estimate, it says furnace blower, blower wheel and run cap)
Is this different run capacitor than the dual one i already purchased?
And is this something that we could replace ourselves possibly, or is it too complicated (we know location of it, usual concerns are the wires and their coloring)

Blower motor is only 206 bucks, so we would same some serious bucks that we don't even have right now.

Supposedly shaft of the motor is bent, which, in turn, caused the wheel to bend and get damaged.I didn't see it, but hubby was on the roof with the guy. Entire house is shaking to the point where mirrors produce vibrating sounds. Roof is shaking, walls are shaking, our wrought iron beds vibrate like nuts. Inside the house sounds like being under a helicopter. It's a very disturbing way to live, but i am grateful to whatever force is keeping this ac going. In arizona, interior temperature can reach well over 100 degrees in about two hours, without ac. I am just happy it's working, even though we keep it on 86, so it operates as least as possible.

Last edited by Sharp Advice; 08-16-13 at 12:05 PM. Reason: Merge Seperate Threads On Same Subject
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Old 08-04-13, 07:41 PM
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Welcome to the forums.

This problem actually started happening after we had a guy do a tune up on our ac
Recently ? Why haven't you had him return if he did something wrong ?

Noise problems are very hard to diagnose without hearing them. You need to determine if the noises you are hearing are present at the rooftop unit.

It almost sounds like you may have a blower issue. Possibly motor bearings or bearings in the blower itself. You'll need to take unit apart and check them.
Old 08-05-13, 05:03 PM
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yes, sounds like a blower issue of a condensing fan motor blade issue. Check for debris in the blower wheel. IF the unit shakes with just the fan set to ON at the thermostat then it is a blower issue. But if it does not shake with the fan set to ON but does shake when the AC runs then it is likely a condensing fan motor blade issue.
Old 08-05-13, 08:19 PM
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No.....turn just the fan on. Leave the A/C off.

If you turn just fan on.....then that's just the inside blower.

We need to determine if it's the inside blower making the noise or the outside condensor fan. It sounds like it's the outside fan making the noise. If the house shakes when in cool mode but not FAN ON then that's telling us the condensor fan is at fault. It could have a bent blade.
Old 08-06-13, 10:32 AM
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You need a new motor and a fan blade to properly repair your system.
Old 08-15-13, 06:25 PM
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I don't understand why he's replacing the entire blower unless it is severely rusted or actually broken. Usually one would replace just the motor (including capacitor) or maybe the motor & blower wheel. If one orders the assembly (if available as an assembly), it would normally come complete.
Old 08-15-13, 06:26 PM
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The furnace blower motor does not come with a blower wheel. Normally the blower wheel is removed from the old motor and installed on the new motor. The only time a blower wheel is replaced is if it gets physically damaged.

The new motor will tell you what size cap it requires. It will be a single capacitor with two lugs....not a dual run three lug cap.

Could you replace it yourself....I would think so. Wiring usually isn't too difficult. Removing the wheel from the old motor could be a little tough if it's stuck on.
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