# Help with noisy A/C compressor



## e_dawg (Jul 28, 2010)

Hi everyone,

I have been scouring the net trying to find an optimal solution to quelling the noise from my noisy outdoor A/C condenser unit, and my search has led me (surprisingly, at least initially) away from HVAC forums and towards acoustics, studio, and HT construction forums.

I have a relatively new (first summer of use, came with the house) 3.5 Ton entry-level KeepRite split central A/C system, and the condenser unit is situated along the side of my house that is adjacent to my neighbour. The compressor noise and vibration is noisy enough that it disturbs both my neighbour and i. Unfortunately, the condenser unit is on the side of my house where the study/library, family room, and HT/music room are. Even worse for my neighbour, her bedroom faces the condenser unit. 

The mid-high frequency buzzing of the compressor and the hash of the fan is not too bothersome as long as the windows are shut tight against their seals, but the low frequency hum and vibration goes right through the ground / wall / foundation such that i can hear and feel it on both the main floor (family rm) and basement (HT/music rm), and my neighbour can hear and feel it in her main floor bedroom. Believe it or not, the condenser unit is sitting on foam-rubber blocks already, yet the vibration seems to go right through them.

I contacted 2 HVAC people in my area, one of whom came to physically inspect the A/C unit, and the consensus conclusions are as follows:

1. I have a cheap condenser unit, which is noisier than premium units as it does not have a dual-stage compressor, the compressor is not mounted to the base of the unit using rubber mounts, and it doesn't have a sound blanket.

2. It is technically possible to move the unit around to the backyard and put it under the deck, but both contractors recommended against it, saying that (a) it would be quite "invasive" and expensive re-routing the lines in the house; (b) there would be too much pressure loss along the line, resulting in low efficiency / cooling power, and (c) placement under the deck would result in restricted airflow, lower efficiency, and potentially just as much noise due to resonance under the deck.

3. The two best solutions from the HVAC contractor's perspective are: (option 1) wrap the compressor unit inside the condenser with a sound blanket and use softer rubber pads under the condenser unit (the foam-rubber blocks seem to be a bit too hard) (cost: $300-400), or (option 2) replace the condenser unit with a premium dual-stage model (cost: $3-4k).

Our neighbour is willing to help us defray some of the cost, depending on how effective the solution is. Naturally, she would only be able to help out so much if we were to spend a fortune on a new premium condenser unit. And my preference obviously is to avoid spending too much money. This has led me to the path I am down now: going with option 1 from an HVAC based solution and supplementing it with sound treatment solutions. It is my hope that the combined solution can give me superior results to getting a new condenser unit at a cost that's much closer to option 1.

Because the condenser is in the "alley" between our two houses, there seems to be a standing wave / resonance effect that is amplifying everything. Furthermore, because the majority of the noise seems to be vibrational from the compressor, i think the focus should be on stopping the noise and vibration at the source: the condenser unit and the virtual "room" created by the walls of our two houses. Ultimately, this means:

1. decoupling the condenser unit from the ground
2. damping resonance of the sheetmetal cabinet of the condenser unit, and 
3. absorbing the standing waves between the two walls

So my questions are: 1. Do you think i have evaluated the issues and possible solutions properly, and 2. How might i best go about implementing the above three tasks?

I have posted a series of pics that illustrate the situation i have described above in the following gallery. Would appreciate if you could take a look and let me know what you think:

http://www.smugmug.com/gallery/13109852_9M9gJ#950588671_JBAxj


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## Ted White (May 4, 2009)

The issues are airborne sound as well as conducted sound through the earth. I might suggest to try and determine if the conducted sound is really a component. Can she hear the system when in her basement?


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## lsiberian (Mar 24, 2009)

I'm with Ted on figuring out if it's airborne or ground borne.


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## e_dawg (Jul 28, 2010)

Yes, she claims that she can hear it in her basement and all the way in the living room at the front of her house. As well, you can readily feel the vibration in your feet walking anywhere along the alleyway and along the floorboards of the study/library, which is the room in my house right next to the condenser unit. Also, you can feel the vibration if you touch the wooden fence and doors that you see in the pics (but i don't know if that's through the ground or through the air).


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## Ted White (May 4, 2009)

OK then a component _may be_ ground conduction. I'd test a heavy, heavy blanket(s) draped over the entire exterior unit and see if that changes things much. This is just a test. The unit may also simply be outputting a frequency that finds resonance with some aspect of the house structure. 

If the very heavy blankets remove most of the problem, then ground conduction can be scratched off the list. That's great, as it means no spring platform system required. That would point to some massive shielding structure / absorption to help


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## e_dawg (Jul 28, 2010)

Believe it or not, i don't have any heavy blankets... only light duvets! Any suggestions on alternatives/substitutes or where to get some cheaply? 

Not to jump too far ahead here, but the "spring platform system" sounds expensive, and the "massive shielding structure" (which doesn't sound cheap either) seems like it would be immediately rejected by the board (aka, my wife) on the grounds of ugliness  Am i over-reacting, or is this a common reaction from newbies? :sweat:


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## bambino (Feb 21, 2010)

Wouldn't it be hard on the unit to wrap it with blankets or heavy material as i thought the system needs to breath?:dontknow:


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## MatrixDweller (Jul 24, 2007)

Maybe a lot of it is the echo off your bricks. Maybe a 4x4 or 4x8 by 2-4" thick panel made of mineral wool board, pressure treated wood (for the frame) and landscaping cloth (to cover it) will eliminate a lot of the echoing. That would cost under $25.


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## e_dawg (Jul 28, 2010)

MatrixDweller said:


> Maybe a lot of it is the echo off your bricks. Maybe a 4x4 or 4x8 by 2-4" thick panel made of mineral wool board, pressure treated wood (for the frame) and landscaping cloth (to cover it) will eliminate a lot of the echoing. That would cost under $25.


I certainly like the price of that option! I'm just trying to visualize how it looks on the side of the house. Aesthetics of the solution needs to be wife-approved too, if you know what i mean. Do you think if i constrain the size of that absorber to the wall surface immediately behind the condenser unit, will that still be effective?

-------

What do you guys think about maximally treating the A/C condenser unit itself? As in, trying to heavily dampen, absorb, and block within the unit itself by:

- putting 2-3 layers of Dynamat on all metal panels
- either using several layers of Dynamat on the compressor or slathering viscoelastic damping compound on the compressor and essentially tiling it with mosaic tile
- wrapping the compressor with a sound blanket (as per all the mid/high end condenser units)
- adding mass to the base (bottom) panel of the unit by putting a couple 10 lb cast iron dumbell weight plates in the compressor chamber
- putting a 3.5" thick fiberglass batting inside the compressor chamber
- mounting the compressor motor with home-made rubber mounts (using a squash ball or vinyl eraser as the donor rubber)

Would these cheapo non-professional solutions focused on damping/absorbing for the condenser unit itself result in any significant gains? The reason i ask is not only to minimize cost, but to minimize any aesthetic impact to the house.


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## Ted White (May 4, 2009)

The blanket concept was a *test* to determine airborne vs. Ground conduction. That's the first step... Identify the problem
_Posted via Mobile Device_


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## tonyvdb (Sep 5, 2007)

I am in the HVAC field and I do not think wrapping the compressor will solve any issues and will most likely overheat it as it was not designed to have a "blanket" around it. The vibration isolation pads under it will help but I would also suggest putting something under the entire condenser unit. My other concern is that the fan is another part of the noise as most older units did not take sound into the equation and the fan blades as they spin chop the air up causing vibration pulses in the air movement. This can be fixed as well by getting the fan blades replaced with more quiet ones that slice through the air much more smoothly.


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## Ted White (May 4, 2009)

Again... the blanket was a test.
_Posted via Mobile Device_


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## tonyvdb (Sep 5, 2007)

Ted White said:


> Again... the blanket was a test.
> _Posted via Mobile Device_


I understand, there is a "sound blanket" that you can buy that is designed to wrap around the compressor but in my experience this only over heats it and causes pre-mature failure.


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## Ted White (May 4, 2009)

Right-O. Which is why I don't think anyone is recommending its use long term. Its a 10 minute test in my mind. 

If the physical blocking of the sound is accomplished with the blanket, we can assume this is primarily airborne noise and design the appropriate suppression system. I suspect your point will still come to haunt him as the space between buildings is tight and that starts getting him closer to closing off airflow around the unit.

If there's no change whatsoever with the heavy blankets (these have to be HEAVY) then we would presume more earth conduction. 
_Posted via Mobile Device_


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## tonyvdb (Sep 5, 2007)

Planting some low 3'tall shrubs around the perimeter of the unit leaving about a foot of space all around can help dramatically as well and still allows for decent airflow.


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## e_dawg (Jul 28, 2010)

tonyvdb said:


> Planting some low 3'tall shrubs around the perimeter of the unit leaving about a foot of space all around can help dramatically as well and still allows for decent airflow.


Hmm... i like that idea! Aesthetically more pleasing than putting acoustic panels up, too. Don't know if we can put shrubs in front of the unit, but maybe ask our neighbour to plant shrubs in front of her wall directly opposite to the unit.


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## e_dawg (Jul 28, 2010)

Ted White said:


> Right-O. Which is why I don't think anyone is recommending its use long term. Its a 10 minute test in my mind.


I think you guys are talking about two different things. Tony was takling about a sound blanket designed to wrap around the 6" diameter x 16" tall cylindrical scroll compressor inside the compressor chamber of the condenser unit, whereas you were talking about throwing wool blankets on top of the entire condenser unit.



> If there's no change whatsoever with the heavy blankets (these have to be HEAVY) then we would presume more earth conduction.


Would anyone know where to buy these large heavy blankets? I don't think this is something you can just pick up at Wal-Mart or Home Depot, is it?


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## Ted White (May 4, 2009)

Consider moving blankets. You can rent them. Again, this is not a solution, only a test.
_Posted via Mobile Device_


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## e_dawg (Jul 28, 2010)

Ah, yes. Moving blankets. Good call. I was afraid i would have to buy all these blankets and then have no use for them (except for maybe 1 blanket) afterwards...


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## bambino (Feb 21, 2010)

Ted White said:


> The blanket concept was a *test* to determine airborne vs. Ground conduction. That's the first step... Identify the problem
> _Posted via Mobile Device_


Ok, i get it i just wasn't following along correctly.onder:


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## MatrixDweller (Jul 24, 2007)

I think you should listen to Tony. The exterior AC unit is designed so that the coolant moves through the system and the thousands of fins help dissipate the heat. Putting a blanket around the unit is not only going to cause the unit to over heat, but it will reduce it efficiency big time.

Replace the fan blades and make sure everything is tight that can be tightened. 

To answer the questions you posted

- putting 2-3 layers of Dynamat on all metal panels
Unless it covers the whole thing the sound will still flank out from somewhere else. It might add more mass to the panels, but it's going to be ugly and will most likely fall off eventually. Dynamat is basically mass loaded vinyl and is not meant for outdoor use. You wouldn't want to surround the whole thing with dynamat or block any of the existing vents (see above)
- either using several layers of Dynamat on the compressor or slathering viscoelastic damping compound on the compressor and essentially tiling it with mosaic tile
Same as my last answer.
- wrapping the compressor with a sound blanket (as per all the mid/high end condenser units)
It will overheat
- adding mass to the base (bottom) panel of the unit by putting a couple 10 lb cast iron dumbell weight plates in the compressor chamber
If you do bolt or glue them down or they might produced more rattling
- putting a 3.5" thick fiberglass batting inside the compressor chamber
You might overheat the compressor
- mounting the compressor motor with home-made rubber mounts (using a squash ball or vinyl eraser as the donor rubber)
Find out the size bolts it uses and either order some rubber or neoprene washers or make your own with a sheet of rubber. www.mcmaster.com has everything under the sun. You could also get them from pretty much any hardware store. You'll want a washer on either side of the bolt between the nut. You might even want to use lock nuts so that it doesn't work free from the vibrations.

The compressor is heavy and after puncturing the squash balls they will "squash" down and be more of a pain to work with (not thick enough either. Vinyl eraser are not tough enough.

So ultimately you could wreck your AC unit doing this stuff to it and then you'll have to buy a new unit. So then end result might be a quieter AC unit after all.


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## Ted White (May 4, 2009)

MatrixDweller said:


> The exterior AC unit is designed so that the coolant moves through the system and the thousands of fins help dissipate the heat. Putting a blanket around the unit is not only going to cause the unit to over heat, but it will reduce it efficiency big time.


I may have missed something, but has anyone proposed using blankets long term? I don't think anyone has.

In my opinion, the OP needs to first determine what the problem is. Airborne vs. conduction. Once that's better understood, a solution will better reveal itself. I would observe there may be a bit too much putting the cart before the horse here.


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## bambino (Feb 21, 2010)

I'ts all my fault Ted, i started back on post #7 with my question. I'll take the blame,LOL:dumbcrazy:addle:


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## e_dawg (Jul 28, 2010)

Guys, i tried putting some moving blankets over it with some difficulty (the airflow forcing its way through made it difficult to fully cover the unit without gaps). Anyways, it was quieter, but the difference was in the mid-high frequency range. It's like if you were to put a blanket over your head. The low frequency droning and throbbing of the compressor was still there, especially when you turn it on. Vibration still travels along the ground a good 10 feet. I am convinced this is a vibration issue -- at least, that's what bothers me. My neighbour is a bit picky in that she doesn't like the fan noise too, but i can't hear it in my house... only the low freq hum and vibration.


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## goyop (May 4, 2010)

Big, loud fans and compressors are big and loud. However I also try to fix everything myself. My recommendation from working with motors and fans is to get the best (not most expensive) isolators for mounting the compressor to the ground. Don't bother with dynamat or complicated wraps. Look up how much you can restrict the airflow around the unit. This is important. If the unit requires a certain amount of airflow, design a simple box to surround it. Make it out of T-111 or some other sheet material and stain it a nice color. Be sure to open enough "vents" to allow proper air flow. Then beyond that plant some shrubs to further muffle the sound. On the inside of the box you can use sound absorbent material like indoor/outdoor carpeting. Get the box above the top of the fan by a foot or two and the mid to high frequencies will not be able to take a straight shot to the neighbor's house.

This will definitely help. Hopefully it will be enough.

What is the make and model of the compressor? Depending upon who it is made by and how old it is you should be able to determine the type of compressor and there may be specs available for SPL levels. If you don't have a scroll type compressor then it is just going to be loud. And if it is an older model or cheaper model the fan will be equally loud.

The newer and higher end compressors are scroll type and are more efficient and much quieter. I know money is an issue as it is for most of us. But you may end up spending tons of time and still end up with a boat anchor. Also, changing the dampers or building an enclosure is time and money. Not to mention that if you damage the compressor or the lines then you are looking at some big dollars too. (I nicked a freon line once trying to save money and it cost me big time)


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## Ted White (May 4, 2009)

e_dawg said:


> Guys, i tried putting some moving blankets over it and it was quieter, but the difference was in the mid-high frequency range. Vibration still travels along the ground a good 10 feet. I am convinced this is a vibration issue


Mounting the HVAC unit on a spring platform will solve that. The key is to have the spring system be of a low enough resonance point to help. This is the problem with arbitrarily using any old rubber for isolation. Generally these solutions will not achieve a low enough resonance to assist.

Try contacting Mason Industries. Tell them your weight load and size and they will tell you which parts you will need. This is how industrial pump systems are isolated.


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## e_dawg (Jul 28, 2010)

Thanks for the advice Ted. Tell me, who would you use to install such a mount system? I guess it would be an HVAC contractor? The two contractors i have talked to are not very keen on this idea. Neither of them said they could source the appropriate parts from their suppliers for me (they said Mason is not one of their suppliers), so I guess i would have to get them myself, but they were also reluctant to install these "mystery" parts instead of the rubber pads they are used to using after i said i could order them myself.

A general contractor or sound treatment engineer wouldn't have the requisite refrigerant handling license, for example, and most HVAC contractors it seems are more keen on selling a new system or throwing a sound blanket on the compressor and calling it a day. I guess at this time of the year, they are too busy to want to take on smaller and more time consuming work that doesn't net them as much profit... :huh:


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## e_dawg (Jul 28, 2010)

goyop said:


> What is the make and model of the compressor? Depending upon who it is made by and how old it is you should be able to determine the type of compressor and there may be specs available for SPL levels. If you don't have a scroll type compressor then it is just going to be loud. And if it is an older model or cheaper model the fan will be equally loud.


The condenser unit is a KeepRite entry level 3.5 ton unit, aka the Builder's Special. It uses a 3.5 Ton Copeland Scroll compressor, model ZR44KA... The fan motor is a GE Commercial unit; i forget what model number it is. I believe the main difference between this entry-level condenser and a more premium single-stage unit is that the premium models have better isolation mounting of the compressor to the condenser unit's base pan and include a sound blanket that wraps around the compressor motor. The even more premium dual-stage units have the obvious advantage of running at low speed most of the time and switching to high speed only when it's hot and humid.


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## Ted White (May 4, 2009)

Contractors often shy away from new things and prefer to do what they've always done. No offense to any contractors out there. 

The problem with "rubbery feet" is that they will easily transmit a vibration. Very easily. Vibration readily conducts through rubber. If I had a sheet of that rubber on your head and struck the rubber with a hammer... you'd be mad. Rubber conducts a vibration very well, especially when compressed under a load, as would be your case. 

The spring system ensures that the resonance of the spring platform is below the resonance of the fan / compressor. This is critical.

The base can be assembled by anyone, but if extensions to the coolant lines, etc are required, then obviously the HVAC contractor will be needed.


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## goyop (May 4, 2010)

From what you found it sounds like you have decent equipment. Although it is not top end but it is OK and I assume it is doing a good job of cooling the house.

As an engineer what I would do if it were my house is the following:

1) Take Ted's good advice and get some good isolation between the unit and the ground. I don't know what the entire unit looks like but if that means isolating the compressor with better mounts or whatever. The more you can decouple the unit from the ground the better for that part of the problem.
2) I am not an HVAC guy, but if compressors can be wrapped with a noise reduction blanket without harming them, then do it. Maybe Ted can recommend a suitable material. If the compressor is exposed to the elements then obviously it has to be weatherproof. Depending upon how much noise comes directly from the compressor this could help a great deal. (I know that several people mentioned this in earlier posts)
3) The last thing I would do for fan noise is build some sort of sound absorbing and nice looking box around the unit. Add the bushes for extra layers and you might be OK. Definitely look up the specs for airflow. It may only tell you that you cannot have anything closer than 36" or something like that. In which case you could build a box around the unit and have the bottom open from the ground to about 6 inches to allow the air to enter and it can exhaust at the top. Some sound absorbing material inside the box will help also. On top of the box you may be able to lay on a piece of wood trellis - the thin slats that criss-cross and is used to box in the lower part of a raised deck or porch. Ted may be able to comment on this but the trellis may break up some of the noise the way a baffle does in any type of muffler.

One last suggestion, if you have one or can borrow one, I strongly advise that you take temperature measurements of all the parts of the system before you make any changes. (Except the isolators) You need to know if you are adversely affecting the performance of the system to a level that will cause it to fail. So get a laser temp gun and shoot all the parts of the system. You will need to note the outside air temperature, time of day, etc., so you can repeat the test later under similar conditions.

I hope you can make it work. Please let me know any progress.


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## goyop (May 4, 2010)

Regarding the blanket, you may be able to order the blanket used on the higher end model of your unit. Definitely find an HVAC guy that will get it for you at cost. Someone on this forum may be able to get it for you. You could also go to the local HVAC place and ask for them to give you a blanket off of an old unit that they may have after doing a new install.

Good luck.


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## e_dawg (Jul 28, 2010)

Just taking a shot in the dark here... does anyone know of any good HVAC contractors in the Toronto, Canada area who might be able to help me? The HVAC contractors i have contacted are reluctant to engage in any "custom" solutions.


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## Ted White (May 4, 2009)

Again, this tact is specifically for ground conduction which you felt was the prime source of vibration transmission. 

It will not improve airborne sound transmission.
_Posted via Mobile Device_


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## the colors (Mar 28, 2008)

Just throwing this out there, but I have seen models mounted to the house a few feet in the air for snow purposes. Mounting with isolators against the house with angle brackets.onder:


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## goyop (May 4, 2010)

If you want install help then drop in on a couple of HVAC places in your neighborhood. You will eventually find someone who will be helpful. If it were me I would drop in and explain that you want to swap out the isolators for some spring types and what do they recommend. If they try to sell you a new AC unit or look at you funny just go to the next place. I use a lot of sub contractors for a wide variety of projects and that is how I find the guys I like. Once you find someone who will help out then get an estimate for the isolators. If you go ahead with the fix then I would ask them about getting you a blanket off an old unit while they are at your place doing the work.

If you want to swap the isolators yourself, you should be able to buy them on the internet. You don't need any license to buy HVAC parts. See if you can find something that is close to the height of the current rubber mounts and/or see how much copper tubing there is for adjustments based upon the new height. I think they leave extra tubing at the compressor and/or run a loop at the end so that there is extra. You may be able to simply lift the unit and swap the isolators. If you want to send photos I will take a look at them.

Decide what you want to do first, e.g., the isolation and then find the right part and decide if you can install it yourself. So if that is your first priority let us know what you find regarding parts. Then send some pix of the current install.


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## bambino (Feb 21, 2010)

goyop said:


> If you want install help then drop in on a couple of HVAC places in your neighborhood. You will eventually find someone who will be helpful. If it were me I would drop in and explain that you want to swap out the isolators for some spring types and what do they recommend. If they try to sell you a new AC unit or look at you funny just go to the next place. I use a lot of sub contractors for a wide variety of projects and that is how I find the guys I like. Once you find someone who will help out then get an estimate for the isolators. If you go ahead with the fix then I would ask them about getting you a blanket off an old unit while they are at your place doing the work.
> 
> If you want to swap the isolators yourself, you should be able to buy them on the internet. You don't need any license to buy HVAC parts. See if you can find something that is close to the height of the current rubber mounts and/or see how much copper tubing there is for adjustments based upon the new height. I think they leave extra tubing at the compressor and/or run a loop at the end so that there is extra. You may be able to simply lift the unit and swap the isolators. If you want to send photos I will take a look at them.
> 
> Decide what you want to do first, e.g., the isolation and then find the right part and decide if you can install it yourself. So if that is your first priority let us know what you find regarding parts. Then send some pix of the current install.


Alot of times you can find guys by doing this, as some will be willing to do "side work". Thats how i got my HVAC installed and for a reasonable price also with a 5 year warrenty.:T


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## e_dawg8 (7 mo ago)

Hi everyone,

A number of years have passed, but I thought it might be useful to provide an update on the situation since I haven't really seen this solution tried / reviewed on the net thus far.

During the pandemic, I had spent more time working from home and decided to experiment. Here's what I did:


Opened up the condenser unit and wrapped the compressor in 3 layers of Dynamat and put the sound blanket back on.
Put 2 layers of Dynamat on the inside of all flat panel surfaces of the condenser. The base pan and back corner were especially resonant, but not after the Dynamat.
Put a foam rubber mat under the condenser unit (the mat is smaller than the footprint of the condenser, so it is not providing any vibrational isolation... it is there to reduce the propagation of sound).
Put a foam rubber mat between the condenser unit and the wall of the house.
Put a bat of rockwool insulation between the condenser unit and the wall of the house.
Put a bat of rockwool insulation in the corners of the alleyway between our two houses.
Put a bat of rockwool insulation on either side of the condenser leaning against the wall.

End result: huge difference. Much, much quieter. In fact, we received a beautiful hand-written letter from our neighbour thanking us for making the AC unit significantly quieter. She said she can finally sleep in her own room at night instead of sleeping in the guest bedroom down the hall. There is still a bit of vibration that lingers but it is audibly much quieter.

The next year, the racoons tore up the bats of rockwool insulation, and the AC condenser unit is still very quiet, so the majority of the difference must be due to wrapping the compressor in Dynamat and treating the panels of the condenser unit.


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