Water Management
How does the water sense circuit work?
Water Management Circuit
The EcoNet enabled furnaces, as well as the non-communicating uses a patented water management system to prevent condensate from the secondary heat exchanger from becoming a problem if something has gone wrong with the trap or drain.
If you look at a furnace in an upflow configuration and focus on the collector box behind the inducer assembly you will see in the bottom left, or top right a water sensor. They each have two grey wires leading to them. The reason there are two is because the furnaces are multi-poise for the most part and whether you install it in an upflow, downflow, horizontal right or horizontal left application, one of those sensors will be at the bottom of the collector box. This prevents you from having to reconfigure the sensor during installation.
The sensor is simply a probe that is inserted into the secondary collector box. The probe is connected to both wires. A small voltage is sent through the water sense circuit and it is looking for either of two things.
1. If water backs up in the collector box it will provide a path to ground (via the metal in the heat exchanger). If the circuit detects this, it will trigger a blocked drain alarm.
T059_F Water Sensed
It will also be displayed on the IFC as a fault 59 on the two 7 segment LED's
OR
2. IF the circuit is disconnected for some reason, it will trigger an alert letting you know the circuit has been tampered with or something is wrong with the circuit wiring or sensors themselves
A059_F Water Sensed
If water is sensed four consecutive times during the same call for heat. It will alternate on the IFC as a fault 59, and a fault 10 (One Hour Lockout) on the two 7 segment LED's.
A058_F Water Circuit Open
This will also be displayed on the IFC as a fault 58 on the two 7 segment LED's
There really is no reason to worry about what kind of voltage is passing through the circuit. You really just need to know how to troubleshoot it.
To test the circuit for sensing water, disconnect one of the plugs from one of the sensors. This should after a small delay, trigger a water circuit open alarm. Rotate the sensor and remove it from the collector box. Reconnect it to the harness and apply the tip of the sensor to an unpainted screw or panel on the furnace and hold it there for at least 10 seconds. It should trip the water sense alert.
If you get one of these alarms, it is time to troubleshoot the actual root cause, not just assume the sensor is bad. The sensor can almost not go bad, and if it did, you have a spare one in the higher side of the collector box (the one that isn’t being used).
Water may back up in the furnace during the initial firing because the trap is dry. Once it trips, it will allow the water to drain into the trap and prime it. This is called auto-priming. So a dry trap can trigger a water sense alert as can any number of other things. The most common cause is failure to put the plug in the back of the trap when the furnace is installed in a horizontal configuration. The plug is found in the kit. There could also be a blockage in the drain line somewhere. The top of the tee outside the furnace is intended to be tall enough that water backs up into the furnace before spilling on the floor. If the drain is not completely blocked but drains slowly, it may cycle on the water sensed fault. Once the blockage is removed, the system will return to operation.
If you are connecting an air conditioning or humidifier drain, its best to apply that separately or down a ways below the vent tee. DO NOT drain the condensate from the coil or humidifier into the vent tee!
An open circuit could be caused if someone disconnects the circuit from the water sensor. This is an intentional fault because some technicians will attempt to get a system going by bypassing the safeties. This of course is a no-no. You may also find a pinched or cut wire, damage to one of the plus where they plug into the sensors or at the furnace control board. Additionally if those all appear OK, you can ohm out each of the sensors. The pins should be shorted. If all else fails, check the pins on the IFC. We have seen where occasional rough tugs on the plug can break the solder connections on the board. If wiggling the socket on the board feels a little like a loose tooth in your small child, then that’s probably the cause.
