EMS Si Wiring Guide and Connection Description


This article applies to the EMS Si Thermostat.


Thermostat to HVAC Equipment

18 AWG          20 AWG          22 AWG

128 ft/380 m                  80 ft/240 m                     50 ft/150 m


Terminal Description and Electrical Ratings

Terminal             Description                                     Voltage                   Current Max

N/C                     Unused                                          N/A N/A

Y                         1st stage compressor                    24VAC 2A

W (O/B)              1st stage heating                           24VAC 2A
or reversing valve

G                        Fan     24VAC 2A

RC                     Cool transformer *                          24VAC 2A

RH                     Heat transformer *                          24VAC 2A

C                       Common                                         24VAC 2A

Y2                     2nd stage compressor                    24VAC 2A

W2 (AUX)         2nd stage heating or                       24VAC 2A
1st stage auxiliary heat

R1+                   Input 1+                                         Temperature/dry contact only

R1-                    Input 1- Temperature/dry contact only

R2+                   Input 2+                                         Temperature/dry contact only

R2-                    Input 2-                                         Temperature/dry contact only

* Factory jumper installed between RC and RH. Remove jumper for 2-transformer applications. See wiring diagrams for additional information.

1-stage heating & cooling system.


Connection diagram for 1-stage furnace with 2-stage cooling.


Connection diagram for 1-stage heat pump with 1-stage auxiliary heat


The wiring diagram illustrates the connections for a 2-stage heat pump with 1-stage auxiliary heat.


Connection diagram for a 2-stage boiler with 1-stage AC.


A connection diagram for a 2-stage heating boiler with 2-stages of AC.


The diagram illustrates the connections for a 1-stage heating boiler with 1-stage A/C and air handler.


Wiring diagram for 2-stage furnace with 1-stage AC



Wiring connections for a 2-stage furnace with 2-stages of AC


Was this article helpful?

Have more questions? Submit a request