Field questions are an important fact-gathering tool. Here are some more commonly asked questions from the field. The answers are provided by Kele Sales Engineers - people who can make a big difference in your project and product performance.

Q: The wiring terminals on many thermostats and packaged HVAC units are designated by letters like R, G, Y and W. What do these letters mean?

A: Most thermostat and HVAC unit manufacturers have adopted a standard terminal designation scheme of letters to identify the control function of their wiring terminals. Here are the most common terminal designations and their typical connections:
 Terminal Designation Typical Connection
R Power connection to transformer (internally connected for heating and cooling)
RC Power connection to cooling transformer
 RH Power connection to heating transfomer
G Fan Control
W1 Stage 1 heating
W2 Stage 2 heating
W3 Stage 3 heating
Y1 Stage 1 cooling
Y2 Stage 2 cooling
Y3 Stage 3 cooling
B Heating damper motor, changeover valve
O Cooling damper motor, changeover valve
E Emergency heat control

Designations for additional functions like remote override, auxiliary relays, clogged filter indication, etc..., are not as standardized from one manufacturer to the next. Also, the common letter designations are often used to refer to wiring colors. The R is for red, G for green, Y for yellow, W for white and so on. . .