24VAC Circuit from thermostat to trigger relay

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  #1  
Old 11-30-01, 08:18 PM
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24VAC Circuit from thermostat to trigger relay

I am trying to install a relay to use with the thermostat. The relay control circuit is 24VAC. I am hooking it up back at the furnace. The 24VAC hot is no problem. I am using the white wire coming back from the thermostat. The Thermostat shorts the red
(24VAC Hot ) to the white wire acting like a switch. What I need is the 24VAC Nuetral. I can get this from the point where the 24VAC transformer connects to the furnace logic board, but I am not sure if that will cause a problem or not. I have placed a
multimeter on those 2 points ( white thermostat wire and 24VAC nuetral in point) and I do get the 24 volts AC only when the thermostat calls for heat. I just want to make sure that using the point where 24VAC nuetral hits the furnace logic board will not
cause a problem when I actually install the relay. I would hate to fry an expensive board in my furnace. If this is not a safe place to install the 24VAC nuetral, is there another one?
 
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  #2  
Old 12-01-01, 06:52 AM
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If I read right

Red to tstat,tstat makes sending 24volts down on white to energize heat.Take the white wire,splice it onto one terminal of the relays coil.When you do this, that terminal will have 2 whites on it.One that continues on to energize your heat and the other to energize your coil.NOW all you have to do is connect the other terminal of the relays coil to COMMON on the transformer.A parallel circuit.Any ???? before you do this give the forum a holler.PDF
 
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Old 12-01-01, 07:00 AM
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If I read right

Red to tstat,tstat makes sending 24 volts,down on white to energize heat.Take white wire,cut it,strip both white wires and place them on one terminal of the relays coil.Now run a separate wire from the other side of the relays coil to COMMON on your transformer.A parallel circuit.Any ??????before you do this?Give the forum aholler back.PDF
 
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Old 12-01-01, 11:12 AM
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I think that is actually what I did. On the terminal where the white tstat wire connects to the furnace, I have attached a 2nd wire which is the 24VAC hot. I also attached a wire to the point where the 24VAC neutral attaches to the furnace logic board. I do not see anyplace where a common is shown on the board, but now that I think about it, there mey be a common. On the bank of terminals where you have R W Y G there is one terminal that has a "C". It is possible that this is common, I will have to get the meter out to check it.

The only difference between the two circuit descriptions is that in your description the relay hot terminal is before the furnace tstat white wire terminal. In mine, the new relay hot wire and the white thermostat white wire meet at the furnace tstat white wire terminal. I can not see why the two ways would make a difference, but then again that is why I am trying to make sure I am doing it right. If putting the relay before the furnace terminal is preferable, why?

Thanks much for your help,

Mike.
 
  #5  
Old 12-01-01, 02:05 PM
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Yep

You are doing the same thing by taking wire from board and connecting the 24 volts to one terminal.Hook 24 volts to one terminal,place another wire on common and touch it to other terminal of the coil.It should energize.PDF
 
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