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Old 02-12-2011, 06:30 PM   #16
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Lennox G8 reads 55volts at W


Now for the good news...

It works! Albeit *slightly* modified

I re-wired the humidifier as before, leaving just the W connection
open (not wired to terminal on furnace). The humidifier is now--
thanks to it's "Blower Activation Feature", running the furnace blower
and humidifying as it should. The furnace also continues to run
properly.

Everything is working fine, except that the W is not connected to the
humidifier as per diagram. I knew this might work, but didn't want to
leave it like this, since it's technically not right.

I'd rather find out the reason for the 55v... but i think it may just
be that this new style humidistat control isn't meant to run with old
furnaces like this.

I'm going to leave it as is and see if i can confirm the Lennox 55volt
W thing as normal, preferably by locating a schematic or at least
finding someone familiar with these units.

FYI i hooked up the humidifier to hot water as recommended since the model 60 runs the blower only while it humidifies (not relying on heat, which it now couldn't do even it wanted to, since W is not connected

:Dan

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Old 02-12-2011, 08:01 PM   #17
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Lennox G8 reads 55volts at W


Ooops.. i keep forgetting that the old fuse used to blow, so the situation can't be totally normal. But i'm not sure if i can keep investigating--maybe beyond me

:Dan
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Old 02-12-2011, 08:15 PM   #18
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Lennox G8 reads 55volts at W


Post some pics of it with both doors off and the cover off the electrical box inside the furnace. Looks like you have an additional transformer/fan relay centre in your first pic. If the original furnace transformer is still hooked up inside the furnace and part of the control circuit then you have a big problem. May also be unsafe to use if the limit control is not wired into the new transformer or gas valve circuit properly.
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Old 02-12-2011, 08:26 PM   #19
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Lennox G8 reads 55volts at W


That furnace is an antique and the heat exchanger is probably cracked. Released in 1968. I had to dig REAL deep to find this, hope it helps.



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Lennox G8 reads 55volts at W-g8-1.jpg   Lennox G8 reads 55volts at W-g8-2.jpg  
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Old 02-13-2011, 05:45 AM   #20
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Lennox G8 reads 55volts at W


Thank you so much for the schematic!! Good thing i stopped working on this last night after that bottle of wine

I am going to check on this "inside" transformer (though i haven't seen one from casual observation) and also, what do you think about testing with a light bulb / pigtail? Could i damage something? I'd like to put a load where i get the reading and see if the bulb lights up.

:Dan
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Old 02-13-2011, 06:24 AM   #21
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Lennox G8 reads 55volts at W


Pics of inside--the W wire is the black one from the block at the top/highest point inside the furnace (it says "24vac" on it so i guess that's the transformer?)

There is 55v coming out of this black wire.

:Dan
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Lennox G8 reads 55volts at W-closeup2b.jpg   Lennox G8 reads 55volts at W-wholething2.jpg   Lennox G8 reads 55volts at W-closeup3b.jpg  
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Old 02-13-2011, 08:22 AM   #22
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Lennox G8 reads 55volts at W


Aha, that extra black transformer with the 2 blue wires on it may be the problem. The power supply 24v should come out of that blue fan centre. You probably have 2) 24 volt transformers in line with each other causing your weird readings. Basically you take the wire from the limit side of the fan control and feed the transformer of the blue fan centre and eliminate the other transformer. The red of the fan centre I believe is normally open and feeds the fan motor for cooling and joins with the wire from the fan part of the fan control (box with 3 wires and white push button) and the brown is normally closed and pigtailed off. Power to the fan control comes directly from the 110 volt supply to the furnace. Then you do the low voltage with W from the tstat to the gas valve and returning to C on the fan centre terminal strip. Remove the wire to the fan motor and cover from the fan control. Start the furnace and run it for 5 minutes and MAKE SURE the limit control cuts the burner out. Make sure you do not have seperate wires going to the tstat on terminals Rc and Rh. Should be a jumper between them. In the OLD days sometimes guys used the original trans for heat Rh and ran another wire for cooling Rc. With a standard 4 wire setup RWYG you remove the old transformer.
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Old 02-13-2011, 01:06 PM   #23
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Lennox G8 reads 55volts at W


Yuri.. the "Blue Fan Center" is the blue outside transformer, right? What is the purpose of this transformer? Was this added later due to A/C?

I'm not sure why the schematic shows 1 transformer yet there are two here?

What is the "limit side of the fan control"? How do i select which wire that is coming from the Fan Control box?

Thank you,
Dan
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Old 02-13-2011, 01:40 PM   #24
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Lennox G8 reads 55volts at W


The blue fan centre is a combo 40 VA transformer and relay to start the fan when running AC and was added later. G energizes that relay. The schematics I gave you are no good now as the wiring needs to be altered. Remove the fan control cover and it will be labelled Fan and Limit and trace the wires accordingly. Do you have an electrician friend who can help you. Hate to see you fry the whole works if you don't rewire it properly or burn the house down because the limit control is not wired in properly.
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Old 02-13-2011, 08:13 PM   #25
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Lennox G8 reads 55volts at W


Yuri.. I am not going to re-wire anything until i'm absolutely sure

Taking measurements to ground shouldn't screw anything up yet... plus i've re-wired an electrical box before (while replacing old wiring with new Romex), so i'm hoping i still got it lol

Tomorrow i'm on the site again and i'll trace the wire to the limit.

I'm still a little confused about something: that blue honeywell box outside the furnace -- you call it a "fan center"-- was added afterwards? To what, then, were all the G,Y,C,W,R wires connected to before? That terminal strip comes out of that blue box!

:Dan
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Old 02-13-2011, 09:11 PM   #26
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Lennox G8 reads 55volts at W


There was no rwygc as those furnaces were not prewired for AC back then. The 2 tstat wires R and W just attached to the gas valve/transformer wires with wire connectors near the elec box, no terminal strip. That is why that fan centre had to be added with the AC as a bigger trans and relay were needed.

You CANNOT check the low voltage 24 volts to ground on those old furnaces as the secondary side of the transformer is NOT grounded like in a modern furnace. Probably why you are getting weird readings. Always need to check to C. CAREFULLY follow my wiring instructions EXACTLY and test the limit control and you should be okay. The schematics are not applicable for that furnace now. That furnace was first sold in 1968, yours is probably a 1978 model and there are no diagrams for it now.
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Old 02-14-2011, 02:00 PM   #27
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Lennox G8 reads 55volts at W


Hi Yuri.. i am going to try your suggestion hopefully tonight. A couple more questions though:

How does the Gas Valve work? There are two blue wires from that black transformer on it and below them are the black (going to W) and faded-white (going to C i'm guessing--will check tonight again). In your suggested re-wire to eliminate the black transformer, will i be tossing the blue wires? Will there be nothing attached to where the blue wires are now on the GV?

The limit control--located in the Fan Control--is a relay to shut off the heat if no fan detected, correct? This will take 5min of burning?

Thanks,
Dan
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Old 02-14-2011, 03:25 PM   #28
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Lennox G8 reads 55volts at W


On the gas valve there are 3 terminals. The middle one is a dud/joining place I believe. The outer 2 are the coil for operating the valve. To test that use your ohmeter. Should be NO continuity between the middle and outer ones. The coil will have some resistance/few ohms. Then use that white and black LVT wire that is on the gas valve and move the white wire to the outer terminal. Then trace it and put the other ends of it on the W and C of the terminal strip of the fan centre. W from the tstat should go to W on the terminal strip and Bob`s yer uncle.

Toss the blue wires and old transformer out. You can watch the dial of the fan control turn as it heats up. Pointer gets to 200 degF and the burner shuts down if everything is wired properly.
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Old 02-14-2011, 06:44 PM   #29
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Lennox G8 reads 55volts at W


I think i've got it all now. Before i make the changes, can you tell me why is the white wire from the gas valve currently on the R on the Fan Center instead of on the C? Is that an error too?
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Old 02-14-2011, 07:01 PM   #30
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Lennox G8 reads 55volts at W


Yep. It is feeding power back to the old transformer and giving you the 55 volts. Gas valve coil goes on W and C.
R feeds the tstat ONLY. Y is to the AC and G turns on the fan with AC.

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