Condensate overflow prevention devices or float switches, as they are often called, are such simple devices that you wouldn't think there would be much room for controversy. In my experience, there are few areas of the trade where technician and installer preferences and opinions vary greatly.

Let's start with some float switch basics.

Float (condensate) switches are designed so that they will remain closed when water is going down the drain as it's supposed to and then open when an overflow condition occurs. For the switch to open, it must be positioned in a location that is normally dry and will reliably fill with water when a drainage issue occurs.

There are very simple switches that just clip onto the edge of primary or secondary drain pans, like the Rectorseal Safe-T-Switch SS3 shown above. When the primary drain overfills, it begins leaking into the secondary pan below. A pan switch like the SS3 will open when the water levels rise. This type of switch can also be used in the primary pan so that it only trips when the water level exceeds the normal levels. In both cases, the switch must be firmly mounted and level to function as designed when the time comes.

Then, there are the more typical devices (like the Safe-T-Switch SS1 and SS2) that are designed to be installed in an aux drain port or sometimes even in the primary drain.

Code Compliance

When it comes to the mechanical code, there is no “nationally adopted code,” but most states and localities adopt the International Mechanical Code (IMC). The IMC is the most widely adopted code in the country, and it states a few things that are important to consider in addition to the general requirements stating that an overflow device is required.

307.2.3.1: “On downflow units and all other coils that do not have a secondary drain or provisions to install a secondary or auxiliary drain pan, a water-level monitoring device shall be installed inside the primary drain pan. This device shall shut off the equipment served if the primary drain becomes restricted. Devices installed in the drain line shall not be permitted.

307.2.5: “Condensate drain lines shall be configured to allow the clearing of blockages and performance of maintenance without having to cut the line.”

So, while that may not apply to you depending on where you live, in general, the Code says:

1. You need to have overflow protection.
2. It needs to be in a secondary pan, in an overflow drain, or in the primary pan UNLESS the unit also has an aux drain line that drains outside or a secondary pan under it. 
3. The primary drain needs to have some sort of cleanout that doesn't require taking the drain apart.

While there are cases when installing simple devices like the SS1 and SS2 in the main drain is permitted, the cases are limited. There is also the issue of buildup collecting on the float itself when it is installed in the main drain. While some technicians swear by the practice of putting the float switch in the main drain line, I generally advise against it.

Installation Practices

So, in most upflow applications, we will install the condensate switch to the aux port on the evaporator coil. When installing the switch, you want to set it in such a way that you accomplish the following:

1. The float trips (rises) before the pan overflows
2. Have free access to the access panels and filter door
3. Water should flow freely to the float if an overflow occurs
4. The float is installed level so it can rise and fall freely 
5. The switch is installed so that it cannot be easily moved into an improper position 

Many technicians swear that if the aux drain is pitched down, water will flow into the float all the time, and they pull the drain perfectly level or even pitched upwards. Others swear that the switch must be mounted directly to the front of the unit. The truth is that the float could be positioned in many different locations so long as you follow the four rules above. It is not the orientation of the PVC connected to the aux port that holds back the water; it is the level of the aux port opening that does that. The level that the water must rise and the total depth of the primary pan varies from model to model. That means that, in some cases, a practice that works just fine on one brand may not work on another.

Many contractors have found that installing a float switch with a flat bottom, like the SS2, right on the front of some shallow coils can result in the pans overflowing before the float trips. Others have found that this same practice can result in difficulty accessing air filters. In these cases, it may make sense to route the aux drain around to the side, pitch the drain down, level it out with 45s, and install the switch there. Like all drains, it must be pitched slightly down for the water to reach its destination reliably, but the switch itself should still be installed level.

Once again, this practice does not result in false tripping because it is the level of the aux drain port that holds back the water, not the pitch of the drain (unless the drain is improperly pitched upward).

Finally, there is a dispute over whether to break the “R” circuit or the “Y” circuit with the switch. It is generally recognized that breaking R is a better practice to prevent short cycling unless the system has another dedicated method for condensate switch connection.

—Bryan

P.S. – To learn more about some extra condensate considerations and practices, check out THIS video.