I just got a central air unit installed in a new construction house.
The unit is mounted on the foundation wall on steel "L" brackets just below
When the unit is operating outside it doesn't seem very loud but inside I
seem to be getting lots of low level vibration (even on the 2nd floor above
the outside unit!)
I've heard suggestions of rubber spacers between the unit and the brackets,
a rubber gasket between the bracket and the foundation, an extention on the
bracket to a triangle shape instead of the "L" etc.
Is any of this worth trying or do I really need to remount it on the ground?
The only issue with the ground mount is that my soil grading hasn't been
done yet so I would need to wait.
I also think I would need to go maybe 4 patio stones thick to get to the
same height as it is now from where I anticipate the fill level will be.
Any problem with that or is making a box filled with crushed stone topped
with one patio stone perhaps a better base than stacking patio stones?
I have only seen a/c units mounted like yours while visiting in upstate
NY. I assume it is for snow, which is not too much of a problem here in
south Texas. However, if you are paying for a new house, you are
entitled to have it fixed right. Putting the unit on patio blocks,
crushed stone or whatever, is not right. Vibration noises inside are not
right either. Insist that the builder get the A/C contractor make it to
your satisfaction, period.
I live up North yes, and hadn't really considered snow as the reason for the
foundation wall mount.
I believe the biggest convenience of the brackets is that you don't have to
worry about the backfill settlement around new construction since it is
right on the wall.
Unfortunately that is causing my vibration issue.
The A/C installation was done with a seperate contractor from my builder.
They visited today, insisted the wall installation was done right and that
the unit was functioning normally and that the best thing to do would be to
get it off the wall and onto the ground (at my further expense of course).
Send pictures of the installation. The way you describe this can not
possibly be correct.
I know of no residential condenser that is designed with clearances that
close. Most require a 2 foot minimum clearance.
I don't have access to a camera at the moment unfortunately so I'll explain
as best I can...
The L brackets have one plane facing downwards attached to the foundation
wall and another running parallel to the ground.
The unit sits on the backside/end of the L furthest away from the house,
likely 2 feet clear of the wall as you mention.
It is bolted directly into the brackets and the brackets are bolted right
into my concrete foundation wall, right below where the brick line is.
\ [ ]
\ (brick) [ A/C ]
\ [ unit ]
| | L bracket
| <---- concrete foundation wall
I have a like setup. I find that occasionally vibration has caused the
unit to move just enough that it is not really evenly set on the brackets
and needs to be moved maybe an inch. When it is solid on the brackets, it
First question is, did you check the hoses to make
sure they were insulated where they run into the
Second, get the damn thing off the wall. When you
get the soil graded right, make a form for a
concrete base for the unit to set on and use ready
mix bags. Depending on weight of the unit, it
should be 3" or so bigger than the base and at
least 4-6" thick. Shim between the base and unit
with redwood or cedar to level if you need extra
height or the concrete base shifts. Mine base
hasn't moved in 25 years and we have lots of
freeze thaw. Then the soil will dampen any
vibration and the only parts attached to the house
are the hoses and electric wires.
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