The air conditioner on the side of my house is on a small slab of concrete. Over time, it has started to tilt as the land has settled. We just recently moved in and a few of the neighbors have givens us advice, almost all of which is different.
What options do I have other than paying someone to remove the unit and re-lay a new foundation for it?
I would try getting a crow bar or 2x4 under the slab and seeing if you could lift it up enough to get some gravel underneath it to level it off. Although this could be difficult if the ground around the slab is soft.
Step 4: Check concrete pad on which condenser rests to make sure it's level. Set carpenters' level front to back and side to side on top of unit. If pad has settled, lift pad with pry bar or piece of 2-by-4, then force gravel or rocks under concrete to level it.
http://home.howstuffworks.com/how-to-maintain-an-air-conditioner2.htm
Dig out some of the front dirt to fashion a down ramp of sorts so you can get a small floor jack under slab. Jack up the slab using a 4x4 long enough to support the entire width of slab. Then, after it's level, put some bricks underneath to support it temporarily. Remove the jack, and make a form to bridge that gap of the ramp area and fill dirt behind it. Mix up some cement and pour in the voids under the slab to hold the bricks in place and support the rest of the slab. Remove form and fill back after concrete is cured.
After doing it this way my slab stayed level for several years.
You might be able to use "Mudjacking", although this would require hiring a professional.
Mudjacking is the process of pumping a water, dirt and cement mixture under a concrete slab in order to lift it. This mixture is called slurry. The exact ingredients vary from company to company, and from job to job. Mudjacking can be the solution to many homeowners’ concrete problems, including foundation settling, crumbling curbs and repairing falling sidewalks. It may also be called concrete leveling, pressure grouting or slabjacking. http://www.wisegeek.com/what-is-mudjacking.htm
Is the unit on legs? If so, the legs might be adjustable.
One bit of caution, some units are actually supposed to be tilted slightly (<1 inch). This is to enable water and snow to drain out the side, versus pooling in the bottom.
Unless your unit is really messed up, you should be able to shim under it.
I would not bother to pay someone to do this. If the tilt is small, why bother anyway?
I would do this the simple way. Pick a spot where you can insert a large crowbar/prybar underneath the edge of the slab, where you will wish to raise it. You may need to dig out a small amount of dirt there to get a firm grip.
In front of that spot, place a piece of wood to use as a point of leverage. It will also prevent the bar from sinking into the ground when you lift. The slab plus the air conditioning unit will be moderately heavy, so expect to need a long prybar to lift it. A friend may be of help here to help you to lift, as well as place a few well placed stones to support the slab after you have raised it to level.
One problem is the slab may crack if it is left without adequate support. To prevent this from happening, after you raise the slab to level, inject some expanding foam insulation into the void under your slab. This foam will expand to fill in that void, providing support for the slab. While you might think that simple foam would be unable to provide much support, remember that it dries to a stiff, hard consistency, and the load per square inch from that slab will not be massive.
I would jack it up with a crowbar or new 2x4. Go to Lowes and get some paver stones to place under there. You may have to dig out a little dirt, but not too much. Make sure the pavers are level.
If possible, buy two metal brackets and mounting hardware from a DIY store (they can help you pick the items) so that you can mount it to the wall a foot or two off the ground. You will need a friend or neighbor to help you lift it; but you will get better air flow, less bottom rusting, and never worry about settling again. (Make sure that the refrigerant lines and power cable are long enough to reach the raised mounting position).
