Honestly, I cannot remember the last time I saw an upright with a secondary drain line. Just recently I see the cut off switches installed where the secondary drain line should be when I inspect some new homes.

As past discussion have went. What if the cut off switch stops working?

The water has no where to go but back down thru the unit and of course there is never a drain pan under them either.

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Ted Menelly
"Castle"
Home Inspection Services