TH8110U1003 tstats with an ST-2E control panel

[MarkJo_FP]

I am having a problem with my dual zone HVAC.
I have 2 TH8110U1003 tstats. One upstairs and one downstairs with an EWC-ST-2E control panel. It is standard Heat and A/C.
The upstairs is the main tstat and seems to function correctly. However, if the downstairs calls for cool when the upstairs is already calling for cool and the upstairs damper is open then it will close the upstairs damper and I have AC running with both dampers closed.
If the upstairs is satisfied and the downstairs calls for cool nothing happens (same thing for heat).

In the checkout procedure for the ST-2E it shows that I should have 24V on the R terminal of the Zone 2 tstat terminal strip when in heating or cooling mode.
The tstats and the control panel are both new and both damper motors work. It seems it has to be in my wiring but I am stumped.

Any help would be greatly appreciated.


The wiring is as follows:

At the upstairs tstat:
Wire color -> Terminal Label

Red -> R
Both White and Blue wires -> W
Both Yellow and Orange wires -> Y
Green -> G
Jumper between R and Rc terminals

At the downstairs tstat:
Wire color -> Terminal Label

Red -> R
White -> W
Yellow -> Y


At the ST-2E panel

System terminal strip
Blue -> Y (this runs into the furnace and I have not opened that. This was wired to the Y terminal on the old MM2 board)
Green -> G
Red -> RC
White -> W
Nothing on the B, O, or X terminals

Zone1 Motor
White(6) -> M6
Green(4) -> M4
Red(1) -> M1
Jumper on motor between 2 and 5

Zone2 Motor
White(6) -> M6
Green(4) -> M4
Red(1) -> M1
Jumper on motor between 2 and 5

Zone-1 tstat terminal
White -> W
Yellow -> Y
Red -> R1
Orange -> O
Blue -> B
Green -> G
Nothing on C or R terminals

Zone-2 tstat terminal
White -> W
Yellow -> Y
Red -> R1
Nothing on C terminal

[MarkJo_FP]

OK - I am starting to figure out a few things. The previous owner put the damper moter arm on 180 degrees from where it should be and wired the zone 2 terminal to the zone 1 damper and vise versa. When I put 24 vAC on terminal 4 of the damper motor it closed the damper and terminal 6 opened the damper.

I have corrected the motor arms and switch the wiring so that zone 1 terminal strip on the control panel is wired to zone 1 damper motor and zone 2 terminal strip is wired to zone 2 motor.

Now everything functions correctly when zone one only is calling for cool or when zone 1 and zone 2 are calling for cool.

However if zone 2 is calling for cool and zone 1 is satisfied the A/C does not turn on.
Same functionality for heat. Zone 2 alone calling for heat does nothing but if zone 1 is also calling for heat the dampers operate appropriately.

Seems like it has to be something simple but I am not seeing it.

[Pcyrana]

Now that you have the damper problem all squared away it seems like your only problem is in the thermostat now.

The reason your zone 2 only works when zone 1 is calling is because the HoneywellTH8110 thermostat is not compatible for zone 1.
The zone 1 thermostat for an ST Panel requires a separate "O" and separate "B" terminal.

When the Operation switch is set to the Cool mode it will output voltage on the "O" terminal allowing the cooling to run in zone 2.
The way you have it wired now, the only time you will have voltage on that "O" terminal is when you are demanding cooling on zone 1.

To fix this problem you need to replace the thermostat in zone 1.

Some compatible thermostats are:
EWC - EWT-3707
White Rodgers - 1F80-361
RobertShaw - 9610
Honeywell - TH4110D

The new thermostat will also need to be wired correctly:

- The "O" and "B" on the thermostat must be wired to the Zone 1 Thermostat terminals "O" and"B" on the Zone Panel.

Please feel free to call if you have any questions.