Through the wall A/C in attic?

I did an inspection a week ago, and found a wall A/C unit that had the exterior side in the attic. It was in a bonus room over the garage. It had a couple supply registers in the room, but apparently the owner didn’t think they were adequate. The unit had a drip pan underneath that was draining to the exterior. It looked odd, so I call it out in the report at a nonstandard installation. I get a call yesterday that the seller is challenging that. After looking through the installation manual online, I can’t find anything that says the exterior side cannot be in an attic. Can this actually be an approved installation??

I suggest checking the installation instructions for that brand/model. Here’s what I found from some installation instructions for this type of AC unit.

To prevent vibration and noise, make sure the unit is installed securely and firmly. Install the unit where the sunlight does not shine directly on the unit. The outside of the cabinet must extend outward for at least 12" and there should be no obstacles, such as a fence or wall, within 20" from the back of the cabinet because it will prevent heat radiation of the condenser. Restriction of outside air will greatly reduce the cooling efficiency of the air conditioner. Install the unit a little slanted so the back is slightly lower than the front (about 1/2"). This will force condensed water to flow to the outside. 5 Install the unit with the bottom about 30"~60" above the floor level.

Your air conditioner is designed to install in standard double hung windows with opening widths of 23 to 36 inches (584 mm to 914 mm) (FIG. 4A , FIG. 4B). Lower sash must open sufficiently to allow a clear vertical opening of 14 inches (356 mm ). Side louvers and the rear of the air conditioner must have clear air space to allow enough airflow through the condenser, for heat removal. The rear of the unit must be outdoors, not inside a building or garage.

Thanks Ken. Do you have a link for those instruction?

It is my recommendation (which pertains to any issues that you call out as a home inspector) is that you identify the problem associated with the issue.

“Because this is a nonstandard installation”; well, you didn’t provide the information but I will assume based upon what I see on a daily basis is that the bonus room does not have adequate return registers, either never there or improperly located. This causes air stratification in the house and you can’t get the heat out. So in fact it’s nonstandard to begin with.

So you go out there and you find something different.
What affect does this issue have upon anything? Utilizing your vast knowledge of HVAC you realize that the machine takes heat from one location and puts it in another.

Now you can’t do this in December because of the weather conditions where you live, but you can hypothesize what can happen in that attic come August.

So the “issue” is: nonstandard installation.

What is the “problem”?:
There are three things to consider. First is the attic cool enough to condense the refrigerant. The second is if the attic is adequately ventilated to remove the heat from the sun and the added heat applied by the air conditioner. Third is what happens to the condensate. Window units use sling fans to get rid of condensate water or allow them to drain out the back of the unit to the exterior. As this is not exterior it’s a consideration.

The first thing I did was look at the drain pan. There is brown stuff (insulation) in the pan that will affect drainage. That would be your concern (if anything).

I really could care less if there’s a building code violation or manufacturer’s installation manual deviation. Those are simply “issues”.
Are they creating a “problem”?

Nothing says you can’t point out that this is odd.
To tell someone they can’t do that or they must spend money changing that is exceeding your scope (in my unprofessional opinion). You’re correct in paying close attention to it but you haven’t mentioned the primary problem.

Crap in the drip pan.

Note non-standard installation in your report. This unit will fail early due to the higher air temps inside that attic compared to being exposed to the outdoor air.