Our home is 6 yrs old, and we have an air conditioning unit (whole house) in our garage. We have a service contract and it is serviced every year by the same company. Each year we have had at least one problem of it getting backed up and water leaking in the garage. Until this year, we did not know (nor had anyone told us) that we should have access to be able to flush bleach, etc into the system to remove the backup--there was never an opening in the piping to do so. Last week, they made the cut and added an elbow joint to provide that access. (It was their third trip in two months due to backups)

However, tonight I went into my daughter's bedroom (it has a shared wall with the garage), and her carpet was soaking wet in a few spots, namely about 12 inches from the wall. VERY wet. We felt along the baseboard, and it felt cold and damp. Then I went into the garage and the unit is leaking profusely.

Should our next step be to call a home inspector, the air conditioner company--both? My daugther happens to suffer from chronic allergy issues, and damp, stagnant water and mold... well... I have to wonder how long we may have had his undetected problem, Who knows how long there may have been mold in her walls, since we get backups every year. Clearly the overflow pipes were not installed with the proper slope (in my mind). Now I assume we are looking at ripping up crpeting and cutting into drywall.

I am not handy with this, which is why I need to know--who to contact first for assistance? Home builder? Home inspector? Air conditioning company? An attorney?

I suggest you have the drain inspected. It should not clog up in that short of time. Also have a float valve or other means of shut off installed in the drain line or pan to prevent the outside unit from running when a drain problem happens

Also it may not be the drain. The unit could be frezing up causing the water. Or it may be a cracked or leaking drain pan in the unit itself.

I hope there drain pan has not cracked in just 6 years.

Me too, but inless the drain runs up hill. I can't see how it would get cloged up in such a short time. I would call the company that installed the system and have been servicing yearly. And show them your service records and demand that they do something about it. If this has been a on going problem sense instulation.

Low charge causing freezing, can cuase a plastic drain pan to crack, seen it a few times. Like Josh said, have the service company out to get this problem fixed.

A heatpump with out a P trap and breather T after the trap in the condensate drain, will make a mess, it can't drain.

We live in FL... no problems with freezing.
Had a friend come over today and he took off the front cover of the Ac unit to look down inside the box the unit sits on (he couldn't see to the bottom through the filter slot if there was water or not). He shone the flashlight then quickly said "holy XX" because it appears there is about 4 inches of water accumulated in the bottom of the box under the unit. An our company (who just came out Sunday) had not even looked for that, nor suggested doing anything about the box--simply rerouting the pipe thinking a pipe had split behind the wall, and any (small) amount of water would eventually dry out. They suggested rerunning the pipes up to the attic (requiring a pump of course) then out of the house. My friend thought that was nuts, to work with gravity instead. At the very least, we need them to take out the unit to get to all the water accumulated in the box, no? I can only imagine the cost... and how much of it we should shoulder--should they take on any costs for missing this?

Can you clarify what box you are speaking of. Maybe post a clear picture of it. There should not be four inches of water anywhere in the system. Is this a downflow unit.

Must be a airhandler setting on a return box. If so best thing would be to cut just a small hole in the box and suck the water up with a shop vac

That's exactly what it is--and they cut open a hole to vac out the water. But the lining/insulation was SATURATED... I am hearing mixed things about replacing the inside of the box since it would take so long to dry--one company said just leave it, it will eventually dry out, the other said to take off the airhandler, get to the box, see what if any water damage is present in the wall (between garage and bedroom that will be exposed when box is removed), then redo box since it was full of so much water for seemingly awhile. I had hoped both would be in agreement.
Thoughts?

Once the water is out, I would just turn the blower to on and let it run constantly for a week. However, you will need to determine why the water was there in the first place, or you will have this problem over and over again and it will never dry out.