Video · AC Repair and Troubleshooting
AC Wet Switch: A Second Layer of Basement Protection
An AC wet switch is a water sensor on the floor beside your furnace and coil that shuts the system off the moment water reaches it. Paired with a drain safety, it protects a basement two ways.
Job footageSwiftPro
- Topic
- AC Repair and Troubleshooting
- Length
- 1:51
- Posted
- July 21, 2026
- Shot by
- The SwiftPro crew, Northern Virginia
What you’re seeing in this video
This is the longest cut of a basement visit. A SwiftPro tech in a black polo and glasses stands by the furnace and ductwork holding up a packaged wet switch. He points to water already on the floor and water flowing backwards through the clogged drain, and explains why that sends them looking for more protection.
The wet switch sits on the floor like a hockey puck, and a soft spot underneath detects water and cuts power to the system. Then he moves to the other half of the setup: the EZ Trap on the drain line, with a pin at the top wired to the control board that pops up and shuts things down when the line clogs.
Two devices, two jobs: one watches the drain, the other watches the floor.
Hey guys, this is Diego with SwiftPro. We noticed that there's water on the floor in this system and that could happen because the drain is clogged. There's something that we can prevent that with and that is with a west switch. We like to put more safeties for water preventions in your home because it could flood over time.
Like we said, it takes about 5 to 20 gallons depending on how often you use your system and the humidity in the home as well. So, this wage is a great thing to use when you have water leaking on the floor that the drain doesn't catch. There's some water around here, a little bit in the system in this drain. We're having a lot of water.
It's coming backwards this way, which is not good. So, you see all this water that is coming down. That is why we recommend to get a wet switch. And the west switch, that's something that it could prevent it.
So, once we connect it to the floor, if there's a little soft spot at the bottom, and when that has or detects or gets touched by water, automatically it turns off your system. Here we have a clog drain. These things are pretty common. Your AC coil, it drains about 5 to 20 gallons a day depending on how often you're using your system and also depending on the humidity in the house and also just, you know, it's a really hot day.
So, you have the system running all day, that could ruin the drain and it can clog it cuz if it gets clogged up and you don't have a safety, which we have here today, we have an easy trap. An easy trap is a great tool to use in here. You just connect it to the drain and it has this little pin at the top and this is also connected to your board on your system. And when this gets clogged up, there's a little trigger here that pops up and then it completely turns off the system.
Once it does that, it will turn off the thermostat and it would explain to you, okay, now you have to come here and say what's going on. And then when you see this come up, give us a call. We'll come out and we'll try to clean the drain or just see what's going
Why it matters in your house
- A finished basement turns a small condensate leak into new carpet, drywall and baseboards. A water sensor at the base of the equipment is about the cheapest protection you can add.
- A wet switch catches what a drain safety misses: a cracked drain pan, a leaking fitting, or water spilling from the cabinet before it ever reaches the trap.
- When either safety trips, the house warms up and the thermostat goes dark. That's annoying, and it's the point. Don't jumper the switch to get cooling back.
What is an HVAC water leak detector and where does it go?
It's a sensor that sits on the floor or in a secondary drain pan and cuts the system's power when it touches water. On a basement furnace and coil it goes at the lowest point right beside the equipment, where a leak shows up first. Some, like the one here, connect to the system itself, so the AC stops instead of just beeping.
Want it done at your place? See AC Repair and Troubleshooting at SwiftPro or call (703) 997-9757.
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