Air condition compressor concrete pad failure

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My central AC compressor unit is outdoor resting on a concrete pad. The pad is 48"x48" in size and 4" thick and it is reinforced with steel rod. I believe the pad is original so that will put it back to 1980 when the house was built.
Recently the concrete pad started to fail. First a crack started about 8 inches from one edge, then more cracks along the outside edges, chunks of concrete started to fall off exposing the rusted steel rods inside. The compressor has four legs and it's bolted to the pad with concrete screws. Of course with the pad failing two of the compressor legs will no longer be resting on anything solid real soon.
Obviously I need to remedy this situation. But I have two questions:
(1) Is it normal for a pad to fail like this after 20 years? Why did it not fail after 8 years or 12 years? If it waited 20 years, does it mean there is some other factor involved? Like perhaps the soil below is yielding due to a sink hole (house is in coastal south Florida sandy soil high water table) or sewer line leak?
(2) If I replace the pad how would I go about doing it? I cannot just lift and move the compressor aside which is very heavy and has very rigid connections into the house's attic. A new pad will take a day have the form done and the concrete poured, then a few more days at least to cure. I will have to wait a while to put the compressor on again...do I get a concrete repair place to fix this or the AC place to fix this?
Thanks,
MC
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Bolted to pad??? How big is the damn thing? High "balsy" crime rate?
If you want to avoid the concrete redo, can you just slip a 4x4 metal plate between the compressor and pad? Maybe that's too "ugly" for you though.
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Thanks for the reply.
I am not sure. The compressor hums and vibrate when it is on. Here is a pic of the compressor and the pad:
http://img.villagephotos.com/p/2005-10/1090906/P1000355.JPG
the model:
http://img.villagephotos.com/p/2005-10/1090906/P1000360.JPG
MC
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Interesting. His 20 year old Lennox has a date code that says it was made 11/96. That's 10 years old. The serial number which he attempted to blank out is 5896K46054.
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to
questions:
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The pad is original, the AC was replaced a little over 10 years ago when I purchased the property.
MC
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miamicuse wrote: ((Snipped))

To answer some of your questions: Pouring a pad is fairly common. Bolting a large compressor may be common but smaller ones like 2-3 tons often are not bolted (certainly mine isn't and most of the ones in my subdivision that I can see simply sit on the pad. Sure a pad can fail after 20 years, especially if there is a lot of vibration. If your machine shakes badly then something isn't balanced. Failure with steel reinforced concrete is probably do to the shaking.
The simplest solution is to simply get 1/8" to 1/4" thick metal 4" wide and long enough to extend from one foot to the next (across the broken edge). Simply unbolt, mark the bolt holes on the two straps, drill the bolt holes, lift one end of the AC(a 2x4 and a pivot point should do it), slip the metal in place under the legs and rebolt.
If you don't want to lift the AC any higher than the thickness of the metal straps, use a 6" wide strap and cut a slot from one edge to the middle the strap so it can slide under the legs.
Then get the AC fixed so it doesn't vibrate so much.
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Call a HVAC firm, they should have the tools and equipment. Some new AC pads are made out of plastic, and work very well. While looking a lot like concrete.
--

Christopher A. Young
You can\'t shout down a troll.
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You could make it easy, get two trex or composit deck boards, one person lifts a side of the compressor, the other person slides in a board. My pads are all plastic.
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In order to explain the situation better here are some pictures:
The compressor resting on the pad:
http://img.villagephotos.com/p/2005-10/1090906/P1000355.JPG
Edges of the pad falling off and a big crack all the way across the front behind the legs.
http://img.villagephotos.com/p/2005-10/1090906/P1000358.JPG
One of the legs resting on the concrete pad where another chuck is about to come off:
http://img.villagephotos.com/p/2005-10/1090906/P1000357.JPG
Model and make of the compressor:
http://img.villagephotos.com/p/2005-10/1090906/P1000360.JPG
LENNOX HS27-036-1P
Any thoughts? A plastic pad?
MC

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house
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Good concrete should last a hundred years, but not all are good. My A/C pad was poured in the 1970s and is still good. Slide something under it that is strong enough and gently pry up and slip some blocks of wood, bricks or what have you under to hold it an inch or more above while you remove and replace the pad.

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Get a 4'x4'x3/4" piece of marine grade plywood, paint with several coats of outdoor polyurethane, then slip under the AC unit.

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Ensure ALL surfaces of the ply are coated with finish.

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all concrete cracks (eventually)
concrete is its hardest at around 100 years of age
consider using Quickrete Concrete Resurfacer on your existing base to repair it, about $25 a bag http://www.quickrete.com/catalog/ConcreteResurfacer.html the resurfacer adheres to concrete something like 3 times better than concrete adheres to itself to itself, and due to the polymers in it, it resists water better than concrete (water seems to be the reason for the spalling of your base)
trowel it on, instruction on how to use concrete resurfacer http://www.quickrete.com/diy/ResurfacingConcrete.html
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wrote:

<snip>
Maybe you can wait until the A/C unit needs to be replaced? If need be you can slide a 4x4 sheet of 3/4" thick external ply under the unit.
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My AC unit, installed 1977, has a precast pad under it. The AC unit is a Carrier round unit and the pad is also round. Maybe you can get a precast pad and slide it under the unit. Or, they do have 2' x 2' precast patio block that are only 1 1/4" thick or there abouts. Four of these might work.
Phisherman wrote:

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Also looks a bit too close to the house. Not enough space between the unit and the wall.
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miamicuse wrote:

You don't "pour" AC pads. They come already poured, much like a huge stepping-stone.
The "legs" you mention aren't legs (I don't think). They seem to be small brackets to keep the unit from "walking" off the pad. The entire bottom of the unit is resting on the concrete pad. In other words, the "legs" support nothing.
Here's what you COULD do: 1. Cut the bolts/screws holding down the "legs." 2. Get a couple of 2x4s under the unit and raise the unit an inch or two. 3. Somehow manage to get the old block out. 4. Slide in a new, plastic, base. 5. Lower the AC unit back in place. 6. Use angle brackets to re-secure the AC unit.
Here's what *I* would do. 1. Ignore the whole thing.
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support
The legs are indeed supporting the weight of the compressor. See this picture:
http://img.villagephotos.com/p/2005-10/1090906/P1000358.JPG
Thanks,
MC
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Well, they shouldn't be. There should be depressions in the bottom of the AC which act as feet.
Might be part of the problem?
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wrote:

Mine isn't bolted to the pad at all. I wish it were, becuase it keeps moving maybe an eighth or fourteenth of an inch every year. Now it is about 2 or 3 inches from where it was 27 years ago. (Maybe it moved slower then and more quickly now. I don't know, and I'm not going to mark it to find out.)
I'm afraid to put it back because I don't want to bend the pipes. But it's only because I'm compulsive that I want to put it back at all. It works fine.

Do you?

People always ask questions like that. Why did my tv break now? The question and answer are above my pay grade.

That might account for a crack, but not for crumbling, afaik.

Right. That's why I'd consider doing nothing until you need a new compressor, now matter how long that is. I'm serious.
Or, since I mentioned how compulsive I am, I might make a wood form, and pour cement under the compressor, just to fill up the empty space where it crumbled away. Same height as current height or if you go a quarter inch higher than the base, no problem. You won't lift the compressor, and when you need a new compressor, you can replace the pad then, if yours is still breaking or not flat after your patch.
Al's idea sounds pretty good too.
IIUC only the parts beyond the steel reinforcing are falling off. Even if it's worse than that, the bulk of the cement pad will be there another 40 years. There is no special reason to think there is a sink hole. Cement cracks and crumbles some times. The AC isn't going to fall to the center of the earth -- it won't fall farther down at all --, and if perchance it does, you can fix it then. I wouldn't go looking for trouble.
After looking at your picture, I agree with myself even more. I would remove the chunks that are an inch away, that have fallen off completely.
And maybe paint the base, if you think that would make it nicer, and before that you could put some kind of spackle in the crack, but unless you want to make it pretty for guests, I'd just remove those totally loose pieces.

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