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furnace transformer
I am trying to wire my furnace so that when the thermostat kicks on the fan runs but not light the gas burner. I have been able to remove a wire that keeps the burner from igninting but the fan won't come on unless the heat exchanger is up to a certain temp. I can't figure out how to go around this. Any ideas?
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so basically you want the fan to turn on when the setpoint on the thermostat drops to a certain point that would normally call for heat. the fan is wired to a plenum limit switch which has a helicoil inside the plenum. there's an aluminum disk that rotates and closes a set of contacts once plenum temperature is reached. so, what you might need to do is install a small 1/2 hp contactor wired in parallel with the plenum switch with a 24 volt control. -
fan control
look at this diagram. it uses a potter brumfield single pole single thro relay with a 24 volt coil. the contacts are wired across the plenum limit. one side is your feed to the plenum switch [relay] and the other is the load terminal to the fan [relay] the coil of the contactor is wired into your 24 volt control circuit. one side is the control neutral the other comes off your thermostat return to the burner relay.Comment
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I wired the switch in the heat exchanger ( tied the two wires together) and the fan does'nt run. The thermostat has a fan only position but I don't know if the furnance has that option. I have the scheme of the furnance but I can't understand it that well. Any ideas?Comment
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scan a pdf file and send it to me.Comment
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You need a heat/cool thermostat and wire it just like you have central A/C, except you obviously will not have a wire run to a condensor.
Heat/cool t-stats have a "fan only" function.
You will definitely need more than two wires between the t-stats and furnace though.
You will need the white and red you have plus a green. The green goes on the G terminal on both the t-stat and furnace.
You'll need to pull a new 3-wire thermostat cable. This is 18/3 cable.
If I were you I'd run 5-wire just in caseLast edited by Speedy Petey; 11-01-2008, 06:35 AM.Comment
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