Heres a good "what do you think happened here...?"
I bought a three year old house a few years back. 1800 square foot single story, master bedroom on the left, then living/dining/kitchen in the middle and two more bedrooms on the right, very wide house. Three car garage in front of the two bedrooms on the right.
It had a bryant gas furnace sideflow in the attic over the master bedroom all the way at the left side of the house, outdoor air conditioning unit all the way on the right side of the house.
Return is also all the way on the right side of the house and way too small...20x30 for an 1800 square foot house. Cheap r4 ducting with a run that was about 45-50' from the return all the way over to the unit, and then supply lines running all the way back. Line set also has to run through the attic all the way from the unit on the right side to the furnace on the left.
Thermostat was also on the right side of the house, which was the north side. The rooms on the left side would get 10-15 degrees colder/warmer than the setpoint before the thermostat would kick off the unit.
Heres the weird part. Two line sets. One was obviously built into the house, goes right into the stucco at the base near the outdoor unit. Those are cut off flush with the house. Second line set ran up the side of the house and then poked through the stucco into the attic. Covered with a sheet metal 3"x3" 12' long cover.
It was a horrible design with the long supply and return ducts and the long line set running through a low attic that hit 140-150+ degrees for most of the summer. During one three week hot spell the air coming out of the supplies was one degree cooler than what was going in and the compressor ran 24x7 the entire time.
I had a few guys out to service the equipment. They were all really mystified as to why someone doing new construction would have set it up that way and why the original line set wasnt used. I never tracked down where that line set ran to.
My best guess is that the furnace was meant to go in the garage, near the a/c unit and the return...but that either the builder or HO didnt want it taking up space out there and asked for it to be put into the attic at the last minute. Would have made more sense to put it in the RIGHT side or in the attic over the garage, but the only supplied attic access was in the left side of the house and it was REALLY hard to get over to the right side due to some vaulted ceilings below...you had to belly crawl.
Or they already had the interior done and the roof complete except for the left side might not have had the tile put on yet.
Last guess is the guy that installed the unit was supposed to put it in the right side and put it in the left side of the attic by accident, and by the time the GC noticed it, it was too late.
Any other theories? This was always a big item of curiosity for me.