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HVAC 214 Electricity For Oil Heat

Fan Center Relays

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Fan Center Relay

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Fan Center Relays

• Designed to provide low voltage control of blower motors and auxiliary circuits.

• Designed to provide a good junction point for other circuits.

• Used on heating systems with air conditioning.

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Fan Center Relays

• Contain the following components:

– A low voltage transformer (step down from 120 to 24 volts)

– A pre-wired multifunction switching relay

– A Low voltage terminal board.

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Fan Centers

• Sometimes used when there are two transformers, one on the heating equipment and one on the cooling equipment.

• These transformers must be isolated from each other based on whether the thermostat is calling for cooling or heating.

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Fan Center Wiring Connections

• Connections:– R is output power from the internal

transformer– 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

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Thermostat calls for heat

• During a call for heat, the normally closed relay contact for the low speed blower stays closed and the blower is controlled by a Fan/Limit switch mounted in the furnace plenum.

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Call for heat

Low speed blower wire goes through N/C contact onto the Fan/Limit

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The thermostat call for cooling

• During a call for cooling, the thermostat closes R to G which energizes the relay coil. When the coil is energized, the N/O contact closes and allows the blower to operate on high speed.

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Call for cooling The high speed blower wire goes through the N/O contact which closes when the coil is energized.

Thermostat closes R to G & R to Y

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Fan Center

• The W, Y, and any additional terminals are just junction points.