Our Carel Homesteam Elite humidifier is activated by a humidistat and a supply plenum pressure sensor in series. The pressure sensor works fine except when all zone dampers are open on a continuous fan setting but no heat/cool. We have verified that the system controller dip switches of the variable speed air handler are set for continuous fan airflow of 50% rather than 35% of maximum.

When all zones are open the pressure sensor does not sense the fan going on and off but instead treats it as off. If we close one zone, it recognizes the pressure and turns the humidifier back on. We have bumped up the air handler speed setting from low to medium (400 cfm/ton), and that has not helped. Carel says we must disable the pressure sensor.

This is easy to do, but it’s a useful safety feature to have the humidifier automatically turn off whenever the fan stops for any reason. We’d like to keep this safeguard if possible. Are there adjustable sensitivity pressure switches for this type of application?

In addition, we want the humidistat to turn on the system fan if it’s not already on. We understand that we need a double-pole relay to respond to the humidistat by connecting both the circuit to the humidifier and the air handler fan to power. But we do not know which terminal(s) at the system controller or air handler will turn on the fan on a zoned 3-ton Trane XL19i heat pump with variable speed air handler.

Can we set this up as we want to or is there any reason why we cannot on this system due to the zoning and variable speed?