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Fan Center

I don't have a diagram but they are easy to wire. Most fan centers have a DP relay. Wire 120v through the NC contacts, through the fan control to the low speed tap on the motor. The NO contact is wired to the high speed tap on the motor. -DF

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  • D luxD lux Posts: 230
    Help wiring fan center

    Its been a long time and I cant remember how to wire a relay in to older gas furnace . Fan Limit 3 wire 110v 3 speed blower Any body have a diagram ? thanks
  • DonDon Posts: 36

    You missed the biggest safty issue. The relay contact (com) should be fed directly from the hot line. The n/o contact would feed the cooling speed fan. The transformer must be the only thing wired to the furnace limit. If multiple speeds are used on the fan care must be taken so that you cannot feed two speeds at the same time. This would cook the motor. If you need to feed two different speeds (heating and cooling) convert the fan/limit control to a 4 wire use. Break out the tab at the bottom, feed hot leg to limit side and n/c contact of relay to fan side. If the relay only has a single feed to relay and transformer take it back and exchange it for one that has two wires.
  • D luxD lux Posts: 230

    there any way to do it with a 3 wire fan limit ? I can do with 4 wire Fan limit I cant seem to find a way with 3 wire limit thanks
  • Dan FoleyDan Foley Posts: 1,019

    If you have a 3-wire fan center (SPDT relay) connect 120v to C, low speed to NC (through the fan control)and high speed to NC.

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  • Here's a diagram

    Look at figure 4 on page 2 for what you need. Unfortunately, as you can see, you need a double pole single throw or double pole double throw fan center relay.
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