MM-2 Mastertrol and wiring Sensi Wifi touch thermostat to Zone 2

whc · September 2021

I have the mm-2 control board on lennox HVAC. i have successfully wired in Sensi thermostat to zone 1 using a relay to separate O/B. works fine. The second zone is the issue. the three wires work the damper for the zone (master Thermostat calls for heat vs cool). i can bring up a C wire, but Sensi thermostat does not power up, indicating that the R wire (T5 on control board) does not carry power. is there a work around here (i have spare wires going to thermostat) to get the new thermostat to work? LOOKING not to have to replace the control board if i don't have to.

whc · September 2021

it seems the Y (T6 on control board) carries power wondering if can swap Y and R at the thermostat connection???

HVACNUT · September 2021

MM-2 control board? Can you post equipment wiring diagram and any zone panels or relays involved?
There should only be 24v at Y if its switched through the thermostat.

whc · September 2021

here is honeywell manual

whc · September 2021

talking about only zone 2

HVACNUT · September 2021

That's an obsolete Master/Slave damper control panel. Time for an upgrade.

ratio · September 2021

The slave stat is switching the common side, not the hot side. I'd suggest using the Sensi to switch two relays & use those to interface with the Mastertrol. You can pick up 24 VAC on terminals 1 & 2 to power the stat.

BTW, there has been some success reported in swapping out the Mastertrol to a TrueZONE panel with the existing Mastertrol actuators, with some rewiring (see https://forum.heatinghelp.com/discussion/155421/wiring-honeywell-hz322-from-a-trol-a-temp-mastertrol-mark-v).