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Thread: Rooftop unit rumbling and whistling

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    DIY Junior Member itsybuggy's Avatar
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    Question Rooftop unit rumbling and whistling

    Hello Everyone!
    Let me start by saying that in May we had Ac tune up by "reputable company" here in Phoenix, and we were advised that our ac unit has to be "trashed" and new one put in place. I was really upset, since ac is about 13 years old, in a good working condition and electric bills were pretty consistent, with no surprises. My husband was pretty upset about me having this guy doing so called Tune up and after living in our home for 9 years, he told me that we can now expect to have problems with the unit, after we had a HVAC company on the roof with nobody else present.
    After we said that there is no way we are replacing our rooftop unit, HVAC guy proceeded to tell us that coils need to be cleaned and that our capacitor is about to fail, which is something we expected, since we had it replaced previously, two years ago with non OEM part, and we already had a Rheem dual capacitor on hand, waiting on this one to die so we can replace it.
    He served us a bill of almost a grand, said that he doesn't expect our ac to work much longer, we said thanks, but no thanks and he left. And what do you know? Two weeks later we started having issues with our AC. It started with very loud whistling noise coming from the vents, when ac comes on. This isn't your normal air blowing when ac is cooling, it's actually so loud that it will wake up entire household during the night, and you have to turn up the tv quite high in order to hear it. Ac continued to blow cold and turn on-turn off cycle works like it always did. Loudness the whistling will go up and down,like it gets muffled for a second or two.
    Then last week, there started rumbling, where we can hear a thunder-like sound coming thru the vents along with a loud whistling we had previously. One half of the house is vibrating while ac is cooling, the other one has a whistle only. It's just crazy.
    My husband went on the roof yesterday and found a crack with cold air escaping from the duct. He sealed it with some expandable foam, but that did not resolve our problem. I looked everywhere online for an answer and can't find any. Calling a professional right now is not an option due to financial difficulties. We are also in the talks with our bank trying to save our home from foreclosure, there is a hefty check from insurance company which is supposed to cover new ac duct and new roof due to hail damage back in 2010, but our attorney doesn't want us mailing that check to the bank until we have signed documents in our hands, so we really have no budget to have this looked at by HVAC guy. Could this be bent fan blades or faulty fan bearings? or could failing capacitor cause this kind of noise throughout the house? Any advice is welcome!

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by itsybuggy View Post
    ...very loud whistling noise coming from the vents...
    ...rumbling, where we can hear a thunder-like sound coming thru the vents...
    One half of the house is vibrating while ac is cooling, the other one has a whistle only...

    Could this be bent fan blades or faulty fan bearings?
    You have a compressor and motor plus a cooling fan and a circulation fan up there, so your different noises could be coming from different components. Maybe you can get the guy who was out a few weeks ago or someone else to take a quick look to see which part might now be making most or all of the noise, but no, a new capacitor is not going to make any difference here. I also dread the day our own old unit will need replaced, but nothing can last forever sitting out in the southern sun.
    Last edited by leejosepho; 08-04-2013 at 03:30 PM.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY Junior Member itsybuggy's Avatar
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    I know Arizona sun is hard on everything, to the point where we gave up on outdoor furniture years ago...But to me concept of the AC unit is similar to fixing your car-just because one part goes bad, you don't trash your entire car, you buy a part and fix the car. I have been in houses here in Phoenix with 20-25 year old ac units which are maintained and fixed when they go bad.. I am sure that our unit can be fixed, but after having it go bad right after having a company come out to do a tune up, last thing we want is to call another one. It's like when you take your car to dealership to have your oil changed and two days later you get stuck on the side of the road with a dead car...So last thing i want to do is call that guy back to tell me what is wrong with my ac, even though i suspect he still remembers what exactly he did to it while alone on the roof. I know they want to sell us brand new units that cost a third of the entire house...His entire visit back in may was nothing but a sales pitch, talking about financing and credit for years and years to come. I should have known and i should have thrown his butt out of the house right away.
    I was hoping someone might chime in with an idea what went bad. My husband and I are pretty handy in DIY projects, but ac is news to us. Parts are very fairly cheap, but i am not sure where to start. To me the little continuing squeak that can be heard thru the vents after ac shuts off, seems like something to do with fan blades being bent or being out of balance...

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The fan to circulate the air into the house continues to run after the compressor turns off on most systems, at least for a short time. This allows the system to use the evaporator's residual temp to continue to cool for a bit. If your thermostat has a separate fan control switch, turn it from auto to on, and see if the noise starts and stops with that fan. The fan may be direct drive, or have a belt. If it has a belt, it may be just replace and retension the belt. Or, it could be a bad bearing on the pulley. Or, it could be the fan motor itself. Without knowing what you have, it's hard to say. A tuneup should not cost $1k, either unless they changed some moderately expensive parts. A clean, and check should be lots less than that, but if they did replace some parts, it might be reasonable.

    There's a separate fan that blows air over the condenser coils when the compressor is running.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member itsybuggy's Avatar
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    When we turned on fan only, it came on just like usual, no noise whatsoever. But it used to be that fan came on for a minute or two before ac started to cool, and then it would continue to run for a minute or two after cooling cycle was done, before unit shut off completely. it's not doing that any more, it just comes on instantly blowing cold, and it shuts of same way. When i turn fan from auto to on, it works okay.
    Tune up cost us 39.99 with coupon, but he really did nothing but give us estimate for either brand new unit or parts that needed to be changed. he said coils needed to be cleaned, he wanted 345 bucks for that, spray costs at Lowes is 6.95. for dual capacitor replacement he wanted additional 475 bucks, we paid for a brand new OEM dual capacitor 17.95 with shipping, so i thought it was very unreasonable what he wanted. his entire visit was nothing but a sales pitch to sell us brand new unit, and when we said no, out old unit started giving us troubles. We didn't change capacitor as of yet, i was told that capacitor would not give us these problems so hubby is holding on to it for now, as he is't really thrilled when he has to mess with electrical things.

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    DIY Junior Member itsybuggy's Avatar
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    Last edited by itsybuggy; 08-04-2013 at 05:07 PM. Reason: Double posting..Oops

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by itsybuggy View Post
    ...similar to fixing your car-just because one part goes bad, you don't trash your entire car, you buy a part and fix the car.
    Agreed, and now it sounds like your circulation fan is not the problem...and since your compressor is the least-likely culprit, I would get someone to take a quick look at the condensor's cooling fan while keeping im mind that getting an oil change for your car does not stop the starter from going out two days later!
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY Junior Member itsybuggy's Avatar
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    I agree about starter and the oil thing, but since hubby and i started changing oil in our cars by ourselves and doing repairs as needed, we had lot less occurrences where our car just stops dead after just spending a day at the dealership Actually we had none!
    It's a well known fact that some dealerships will fix one thing while messing with the other to keep you coming. Hence i am convinced that same goes with other trades. Not everyone out there is bad, but bigger companies are not that big for no reason. I am sure 100% that the guy did something to our ac in hopes we will call him back to fix it. I will have my hubby check out that fan, thank you!

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by itsybuggy View Post
    I am sure 100% that the guy did something to our ac in hopes we will call him back to fix it. I will have my hubby check out that fan, thank you!
    Your initial post left me with the impression you suspected some kind of foul play, but that condensor fan almost certainly has a sealed motor that would be difficult to damage without leaving some kind of physical evidence.

    Tell your hubby to shut off the power to the A/C so he can safely reach the fan blades with a thin stick or whatever to give them a spin and see how freely they turn. If the bearings in that motor are bad, that fan will likely not spin very freely for long at all (if at all) and might even sound bad without the motor ever being started.
    Last edited by leejosepho; 08-04-2013 at 05:56 PM.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY Junior Member itsybuggy's Avatar
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    Thank you, we will do that! How long do we have with it if fan motor bearings are bad? Money is really really tight.. Also, is this the kind of part i will be looking for if fan motor is our issue?Name:  41wV-fa6uDL._SL500_AA300_.jpg
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    DIY scratch-pad engineer leejosepho's Avatar
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    Yes, the motor you will be looking for will likely look something like that. With the particulars from the A/C unit's nameplate in hand, you might be able to do some online searching that could be helpful in locating one if that proves to be what you need.

    Quote Originally Posted by itsybuggy View Post
    How long do we have with it if fan motor bearings are bad?
    Possibly until about noon today...but nobody can know for sure until the bearings (once again) overheat to a point of (continuing the process of) melting things that were never intended to melt or to throw sparks or whatever. And unlike with you car where you can possibly see the smoke beginning to come out, this motor inside a cabinet up on your roof could easily "lose all its smoke" and begin causing even bigger trouble without ever being noticed until after "the crash". Not meaning to be an alarmist here, but I would likely shut the entire thing down and open the windows at night to try to cool the house down a bit for the next day.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY Junior Member itsybuggy's Avatar
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    So hubby was up there with the stick, he pushed the fan slightly and fan continued to spin freely without any effort. He said there is no noise or any kind of grinding that could be heard, and this was with unit off. Then he had me turn ac on, and he was looking at the fan, he said other than for fan appearing to be slightly shaky and out of balance there was still no grinding noise of any kind. Actually, only noise that there is, can be heard only throughout the vents, up on the roof, everything sounds normal. We have a HVAC guy coming in the morning to check it out. Our AC basically sounds like a Harley motorcycle, but only inside the house; it is super weird. Sometimes i wonder what did insurance adjuster do to inspect the actual ac unit, and if he maybe unscrewed something that he wasn't able to properly out back together...I guess mystery will be solved tomorrow. If it's, in fact fan motor, we have general idea how to change it, thanks to You Tube. As for opening windows at night,,,that's a good one! We live in Phoenix, AZ, where at night there is about zero breeze, and even if there is some, it feels like microwave, even at 3 am. If i ever needed luck on my side, this is the time! I will let you know what transpired, we are at the loss, since everything up there seems just dandy.

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