EWC ST-2 and Honeywell T87K and T87N

[Keith1415]

Hello,
I have an EWC ST-2 2 zone controller and the Honeywell T87K and T87N thermostats. I am having problems with my newly installed central air. The EWC ST-2 works perfectly with the heating, confirming that the dampers are both functioning properly. With respect to the cooling, the thermostat with the subbase works properly and will open and close the damper in Zone 1 if it needs cooling or if it is satisfied, respectively. However, the Zone 2 thermostat does not seem to respond and constantly cools even if the room temperature is well below the temperature setpoint on the thermostat (the damper stays open and the system is constantly running and never turns off). One night I set the thermostat to 72 and woke up 4 hours later and the room was at 56 degrees! Like I said before, the thermostat works properly for heat, so I don't think it is malfunctioning. It claims to be a heat only thermostat but the wiring diagram for the EWC ST-2 says that you only need the W, Y, and R wires, which are the ones that are in the heat only thermostat. So I am wondering whether or not this sounds like a wiring problem or if the thermostat just isn't compatible with the EWC ST-2. I don't know a whole lot about this, but from what I have seen online even if I were to buy a heating/cooling thermostat for Zone 2, you are only using the same three wires as on a heat only thermostat. So what does it matter? Any help/advice would be much appreciated! Thank you.

Keith

[Pcyrana]

Keith,

The new Honeywell T87 thermostats are "power-stealing" thermostats and therefor will not work with the ST series of panels. This is the cause of your cooling running constantly. In order for the Zone Panel to work properly you will need to replace all power-stealing thermostats with non power stealing thermostats.
If you need help selecting the correct thermostats feel free to call.