The terminals on the SPDT switch are color-coded. The red terminal is the common, the blue terminal opens on a temperature increase, and the yellow terminal closes on a temperature increase. See Figure 2 and Figure 3 for standard wiring.
Figure 1. Switch terminals and screws
Callout | Description |
---|---|
1 | Adjustment screw |
2 | Clamp screw |
Y | Yellow terminal |
B | Blue terminal |
R | Red terminal, common |
Figure 2. A19 Series switch action for single-pole, double-throw
(SPDT)

Note: The red (R) to yellow (Y) contact closes when hot water circulates.
The red to blue (B) contact closes when cold water circulates.
Make all wiring connections with copper conductors only, and in accordance with the local, national, and regional regulations.
Important: Use the terminal screws furnished
(8-32 x 1/4 in. binder head). Substitution of other screws could cause problems in
making correct connections.
Figure 3. Wiring diagram for a standard heating and cooling circuit
Callout | Description |
---|---|
1 | A19 control |
2 | Line voltage heating and cooling thermostat |
3 | Speed control, if used |
4 | Fan motor |