Schematic question

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Old 02-12-08, 11:22 AM
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Schematic question

this is my exisitng furnace heat schematic.

The schematic on the furnace shows the leads a and b reversed from this diagram.

If I change these leads will the furnace still work ? ie move a to b and b to a

as in W to Rh ?
this was setup this way by the a/c ppl when they put the a/c into the furnace.



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Old 02-12-08, 11:58 AM
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If all you use the furnace for is heating then it should be ok either way. The t-stat is just a switch.
 
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Old 02-12-08, 11:59 AM
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It will work either way.

The convention is to have the transformer (hot) lead use a red wire and it will connect to the R or Rh terminal on the thermostat with a white wire connecting to the W or W1 terminal on the thermostat and back to the W terminal on the furnace.

You may also have a green wire that connects to the G terminal on the thermostat and to a G terminal on the furnace. This is for manual blower operation. If you do have the green wire and the thermostat has an "Auto-Fan-On" switch then the red lead from the transformer must be in on the R (or Rh) terminal of the thermostat.
 
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Old 02-12-08, 12:08 PM
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thanks guys excactly what I was looking for ...

when they put in the a/c they added a second transformer -- most likley cause they didn't know lennox -- the a/c guy was york

so they took a quick way to get it all working
my suspicion

-- so there are 2 transformers in the furnace 1 for G and Y the second only for W

once I get this rewired I want to put it all together to have only 1 transformer.
 
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Old 02-12-08, 12:43 PM
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once I get this rewired I want to put it all together to have only 1 transformer.
I would advise against that. There are several reasons why having two transformers is better.

In fact, if it works, even if the wire colors are incorrect, why change it?
 
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Old 02-13-08, 07:21 AM
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the wiring seems to be mmessy and haphazard in the furnace,

are there a special kind of terminal contector to connect wires in a furnace or do the twist and turn on caps work fine?

I suspected that the two transformers may be affecting the furnaces habit to eat an ignitor module every few years... plus the drum humidifier was hooked of 1 of the transformers which 1 of the service guys said could affect the module ? can that ?
 
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Old 02-13-08, 07:24 PM
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after thinking about this I relaize that on one side I have a few relays and a transformer G and Y

on the second transformer I have W or the heat leg

why can't both be on a single transformer it would cut out the 40va and 75 va tranformer to a single 40 va transformer for the entire furnace

power saving as well as integrated operation ? or not ?
 
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Old 02-14-08, 02:12 PM
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You could re-wire using just the single 75 VA transformer...if you know what you are doing.

I couldn't begin to advise you on how to accomplish this without knowing ALL of the different equipment in your system and how it is currently connected.
 
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Old 02-14-08, 04:26 PM
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ok

I'm not going to make any changes till this summer -- no need to run into trouble till the heatg season is done

so this is the schematic of the exsitng furnace
2 transformers the orginal a 24v 40va on the fan control center hooked o the fan motor and to the a/c unit relay

the other side is hooked to a 75va trans with onlt the inverted heat circuit.



I would also like to add a second relay to hook in the humidifier so I was looking at a white rodgers 90-130 fan control center with dpdt relay latter --

I think I need to invert the heat system first , on exisiting transformer , the 75 va (honeywell af150 ) unit== this will put it in place like on the furnace schematic
 
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Old 02-14-08, 08:52 PM
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Remove the 40 VA transformer.

Re-connect the hot lead from the 75 VA transformer to the Rh terminal of the thermostat. Connect a jumper wire between the Rh and Rc terminals on the thermostat.

Connect the common leads from the A/C and fan relays to the common of the 75 VA transformer.

I assume that the humidifier requires 120 volts for its operation. Some furnace boards have a terminal for this purpose and it is energized with the fan operation.
 
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Old 02-15-08, 08:36 AM
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ok think i got you thanks again ,

schematically this is the result ,
the tstat is now jumpered and the wire going to Rc is taped up at the tsat...

in reality ----I'll use my skills from working as a reseach lab technican to help pull me thru the real world wiring part---

the 75va transformer was put in by a service tech since it was the only one he had in the truck at the time --- the previous one was a 40 va with a buss fuze

there seem not to be any boards in this furnace -its a 1963 design but made and installed about 1991 -- why ask the contrator

next the power side.



thiss makes Dave and me happy !!
 

Last edited by geoimpala; 02-15-08 at 09:38 AM.
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Old 02-15-08, 10:13 AM
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on the power side (120 v) I have the following .

I have a question about the l4064 -it has 4 wires 2 red that go in the 24 v circuit, I assume but can't check right now that the other 2 ylw and blk are the hot 120 v wires to the fan control. ? right / wrong ?


here is what I have now '




and this is my target configuration using the 90-130 fan center with dpdt



this should make Dave (lennox ) and me happy as I now have high speed summer fan motor as well as low speed winter as recomended on the schematic in the furnace.

did I get this right ?
 
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Old 02-15-08, 11:21 AM
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Wink

I would also like to add a second relay to hook in the humidifier
Just get a A 50 and slip it over the blower wire. Or a sail switch both will control it for you.
 
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Old 02-21-08, 11:13 AM
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Thanks for all the good info guys , I can really start plotting my actions with that--

There is one more question with regaurds to the 2 transformers.

I have read that the g8 furnace even my 1990 built one can, when both a/c and heat are in it, trip or override the upper safe limit on the limit switch when the fan is on from the thermostat with a single transformer ...

is that right ? and could someone possible tell me why ?

thanks good enough reason to leave it alone hahah
 
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