HVAC214 – Electrical for Oil

1. HVAC214 – Electrical for Oil Fan Centers

2. Fan Centers • Designed to provide low voltage control of blower motors and auxiliary circuits. • Provide a good junction point for other circuits. • Used on heating, cooling and air conditioning systems.

3. Fan Centers • Contain: • a low voltage transformer (step down from 120 to 24 volts) • Has a multifunction switching relay • Low voltage terminal board.

4. Fan Centers • Sometimes used when there are two transformers, one on the heating and one on the cooling side. These transformers must be isolated based on what the system is doing.

5. Fan Centers • These notes are based on the Figure 2, on page 2 of the Tradeline manual attached to your notes. • This is a diagram of a heating and cooling application with a two speed fan. • Cooling high speed • Heating low speed

6. Fan Center

7. Fan Center • Connections: • W is the junction point for W from tstat and W from equipment • G is the connection from G from the thermostat • Y is a junction point from for Y from the t-stat • C is common from internal transformer • R is power from internal transformer

8. Fan Center • In a call for heat the normally closed relay to the blower is closed and the fan is controlled by a secondary switch in the furnace plenum. • In a call for cool, green is energized and brings the fan in on high speed.

9. Fan Center • The W, Y, and any additional terminals are just junction points. • Remember, transformers in series double the voltage. • Transformers in parallel double the amperage available.

10. Fan Center Burner Control R L1 ----> G Fan High Y Fan Limit Then Fan Low W Tstat (opt) Condenser