It's called an AC pan condensate float switch because it floats.
There are many detection devices to hopefully avoid a leak problem from a clog in the AC condensate drain line or drip pan.
One of those devices is a float switch which turns the unit off if there is a clog.
All HVAC units have a primary condensate drain line which sends the collected AC condensation to the outdoors or a sump pump.
Best practice would have a drip pan underneath the HVAC unit with a secondary overflow line attached which would send any water collected from the drip pan also to the outdoors, usually via gravity.
The often drip water in front of a window so when there is a clog in the drain pan it can be detected.
However, both the primary and secondary drain lines can clog, and so there is a further fail-safe way to protect the house.
In a circumstance where both lines clog there are devices to shut the unit off so no more condensation can be created which would overflow the drip pan. Hopefully these devices avoid flooding the house with that water.
In this subject house, new construction, the secondary line attached to the drip pan was never sent anywhere, capped off beside the water heater that was right beside the unit, as indicated by the upper red arrow.
So, the builder had a safety float device installed. It works such that if the drip pan should fill with water the float will rise with the water level and turn the unit off.
But if the float it outside the pan how will it rise with any water collected in the pan? My thinking is that it will not. No water, no float.
Now, if the float device was INSIDE the drip pan it might work as intended.
My recommendation: new construction can reveal some interesting things! The county had obviously approved this HVAC installation. The supervisor supposedly had signed off on it, being there every day to insure things were done properly. And the HVAC professional is supposed to know how things work. But somehow this slipped by! Cleaning the drip pan, moving the device forward to the foot of the unit won't interfere with the float, and then moving the float to the inside of the pan would go a long way toward an installation that meets the device's instructions.
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560