I had someone out today to clean my A/C evap coil and check the refrigerant level. They recommended installing a float switch in the condensation drain that cuts it off if the drain gets clogged to prevent water damage. I have never heard of this happening. Am I correct in assuming this isn't necessary? I did opt to NOT have it done.
It can definitely happen. Most AC units as far as I know have one of two setups.
Setup 1: The pan has one drain and a float switch. If the drain is clogged, the float switch turns off the AC. If the float switch breaks and the drain is clogged you're dealing with a flood.
Setup 2: The pan has a primary drain, and a secondary drain a bit higher in the pan that leads somewhere obvious like over a sink or over the back door of the house outside. If the primary drain clogs, the secondary drain comes out somewhere you'll notice. If both drains clog, or you don't know that's what's happening when the secondary drain starts working and it eventually clogs, you're dealing with a flood.
I just cleaned out the primary drain from my girlfriend's parents house because I noticed a lot of water coming out of a pipe over their back door. They had noticed it but had no clue what it was, so were ignoring it. If that pipe had clogged their AC in the attic would've flooded and been a huge problem. In college we had a drain over our bathroom sink that regularly dripped water, I'm sure now it was the secondary drain. We had no clue at the time and lived with it for two years. The maintenance guys didn't even know what it was (apartment maintenance in a college town).
The great thing about float valves is the AC stops working, and you can't really ignore that. Then again I had a friend whose float valve malfunctioned and the drain clogged and it flooded his house on the second floor (down into the ceiling of the first). Neither is perfect, but I'd be very cautious only having one drain with no backup plan. They can and do get clogged, although a bit of bleach down them once in awhile supposedly helps.
