# Lennox G8 reads 55volts at W



## Dan Martinic (Feb 8, 2011)

Hello.. an older Lennox G8 furnace is reading 55volts at W measured across C. Apparently, it's been this way for a while. 

I see some Lennox pros on here.

Before the old house fuse box was replaced, the furnace fuse would blow regularly. The new circuit breaker box and breaker doesn't, however.

Common problem? Where to start?

Thank you,
Dan


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## yuri (Nov 29, 2008)

What is the secondary voltage from the transformer with no load on it. Check with wires removed. Should be 24 volts or higher. After that you either have a weak transformer or bad thermostat wiring between the furnace and thermostat and or poor connections or both. Do you have AC in the furnace. Should have a 40va 24 transformer not the smaller one that came with the furnace.


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## Dan Martinic (Feb 8, 2011)

I'm not at site; will check stand-alone voltage later this week.. but i did remove the thermostat wires and was still getting the bad reading on W. Don't want to change the transformer if not necessary.

Yes, there is AC and i'll check the transformer spec--it does look original (Honeywell) but a decent size. It's buzzing pretty bad btw.

an


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## yuri (Nov 29, 2008)

Thats an OLD furnace 20+ years. Transformers can die from old age. Buzzing means the plates and rivets holding it together are coming loose. Transformers are cheap. Under $50 should get you one at Graingers/ Johnstones. Need to check the incoming primary voltage. Needs to be at least 110 volts.


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## marchvac (Nov 29, 2009)

If it has a transformer hooked up to the fan for humidifier it might do that. you would have to hook up the transformer for the humidifier to line voltage and add a curent sensing relay or air proving switch.


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## Dan Martinic (Feb 8, 2011)

Funny you should say that... ...i came across this problem while installing an Aprilaire 500 with new model #60 control. I wired it all up as per diagram and the furnace ran and wouldn't stop until i disconnected C or W from humidifier.

The new Model #60 humidistat is wired to a separate transformer that opens the water solonoid; power comes from furnace R and C, and G is re-directed from thermostat to humidistat then back to furnace (the humidistat now has the ability to turn on the blower without a call for heat).

In any case, i disconnected the humidistat and still getting 55v across W and C at furnace.

I may just start by replacing the transformer but first, anyone know if i could check for a stuck / open relay in the furnace? Anyone familiar with this model? Where could i take some more measurements?

Thanks, Dan


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## yuri (Nov 29, 2008)

55 should be impossible ( I was thinkin 5.5 earlier and not reading well) as the maximum the trans can produce is 24 unless it is shorted. That high a voltage should burn out the tstat etc. You may have some kind of backfeed or your meter is reading improper? not measuring DC volts R U?

Try going from C to a copper water line. Try the furnace neutral to a copper water line also. Should have no volts or under 3. You may have an unbalanced or live neutral or other problem with your house wiring. Need an electrician or one of the other guys here to talk you thru that problem.


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## Dan Martinic (Feb 8, 2011)

I'm back on site and i've got 5volts from W to ground (furnace cabinet or electrical box). I don't think that's good. What's more likely, a transformer issue, or house-wiring? How can i test the transformer again?

Thank you,
Dan


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## Hubcap626 (Feb 12, 2011)

Pull the wires from the 24v side of the transformer. Go to the common and hot and if you don't have 24v it's a bad transformer, that is if the incoming is at the correct voltage.


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## Dan Martinic (Feb 8, 2011)

Before i do that, let me add something--can't believe i didn't check this before.

I just removed the wire from W that comes out of the furnace itself--making the W terminal completely bare (i only removed the thermostat wire before).

No 55volts anymore on W.

BUT.. there is 55volts on the wire coming out of the furnace.

Is this some old Lennox design? Why would the furnace be feeding the W terminal 55volts all the time? And how does the furnace work normally? That is, the furnace is feeding 55volts to W constantly.. but it only calls for heat when the thermostat calls? When the furnace was running earlier blowing heat, W measured the same 55volts.

What's going on?!?

an


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## Dan Martinic (Feb 8, 2011)

Wired it all back up. Getting 26 volts on W while heat is on, 55volts idle.

If this is normal for this old furnace, then the Aprilaire model 60 humidistat can't work as directed and i'll have to wire it up like an older model 58 or something--losing the Blower Activation feature 

Any thoughts?

an


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## yuri (Nov 29, 2008)

Post the complete model #. Also the complete serial #. There was a G8E and other variations.


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## Hubcap626 (Feb 12, 2011)

Seems to me a common wire isn't tied in right somewhere. Trace that wire and see where it goes if anything is tied into it that shouldn't be.


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## Dan Martinic (Feb 8, 2011)

The wire from the furnace to the W terminal is connected goes into the furnace and connects to a screw with nothing else on it. There are some teeny copper lines, a yellow wire on its own screw, and 2 thicker blue wires with push-on leads. The yellow and blue go down into the blower department.

Looks all original and right though.

an


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## Dan Martinic (Feb 8, 2011)

The Model number is: G8D2-82-4

The Serial number is totally blank, and a paper sticker below is long gone.

Wish i could find a schematic for this sucker!

an


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## Dan Martinic (Feb 8, 2011)

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 

an


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## Dan Martinic (Feb 8, 2011)

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 

an


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## yuri (Nov 29, 2008)

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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## yuri (Nov 29, 2008)

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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## Dan Martinic (Feb 8, 2011)

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.

an


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## Dan Martinic (Feb 8, 2011)

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.

an


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## yuri (Nov 29, 2008)

Aha,:detective: 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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## Dan Martinic (Feb 8, 2011)

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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## yuri (Nov 29, 2008)

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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## Dan Martinic (Feb 8, 2011)

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!

an


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## yuri (Nov 29, 2008)

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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## Dan Martinic (Feb 8, 2011)

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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## yuri (Nov 29, 2008)

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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## Dan Martinic (Feb 8, 2011)

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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## yuri (Nov 29, 2008)

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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## Dan Martinic (Feb 8, 2011)

I am totally understanding it better now. Thanks so much! Didn't do anything with it last night.. valentine's day.. obligations 

I'll be here again next week at which time i'll do the re-wire and report back. Thanks again Yuri.

an

PS: i made a little youtube video of the 55 volt measurement.. check it out.. that's the Fan Center buzzing! http://www.youtube.com/watch?v=n7ZdoPz_yOk


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## Dan Martinic (Feb 8, 2011)

Yuri.. what if i simply put the white from the gas valve to C instead of R as it is now? I am still curious why the old transformer was left in to power the gas valve.. is there a good reason to do that?


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## yuri (Nov 29, 2008)

You sound dangerous to me and I don't take kindly to people questioning my instructions. DON'T overthink and follow my instructions EXACTLY. I am leery of you burning your house down by fooling around with your wiring. The old transformer comes with the furnace and is too small to power a fan relay. The fan centre has a bigger transformer. I won't babysit you thru repairing it if you fry it or spend hours teaching you HVAC wiring as you don't know any of the components or what they do. There are Community colleges for that.


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## Dan Martinic (Feb 8, 2011)

Yikes! I'm not questioning your instructions.. i apologize if it appears that way. Just making sure that there isn't a reason that transformer was left in there. After all.. another tech installed the Fan Center lol

Your instructions are fantastic and i thank you for them. The only part that still confuses me a bit is that the "brown wire is closed and pigtailed off". Not sure what you mean by "pigtailed"? The way i picture it, it seems open to me. I know i'm wrong; just wish to know why.

an <-- totally not dangerous.. ..unless cooking dinner


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## yuri (Nov 29, 2008)

Sorry Man, I am used to training apprentices with some basic knowledge of what we are working with. I cannot help you if I feel you are not following instructions properly and cannot hold your hand over the net and connect the wires for you. I am not sure what the original guy was thinking but it was done wrong and w/o being there cannot straighten it out. I have told you exactly how to wire it and am not going to answer everyone of your questions. Get a tech to wire it for you and make sure all the controls are working properly. The fan centre may be damaged by this setup you have and there is no way I feel this job is going to turn out safely for you or the next guy who buys your house if you leave it miswired. I have dealt with too many DIYers who think a furnace is some fun project like a lawnmower to play with. You don't know what is going on there so get someone who does.


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## Dan Martinic (Feb 8, 2011)

Fair enough.. thanks for all of your efforts. If i decide to call a tech in, at least i know what to tell him.

Now.. all i need to do is find a tech that a) knows the old furnaces, b) is competent, and c) is honest.

Apparently... like most trades, it's hit and miss. And i'm not much of a gambler.

Thanks again,
an


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## Dan Martinic (Feb 8, 2011)

Just wanted to thank you for the instructions. I decided to try the fix myself. Finished the re-wire last night. All works perfect. Since you weren't 100% sure about the gv, I did some research on Honeywell gas valves and confirmed your description. You were right about the terminals TH/TR etc.

The original tech who installed the A/C basically followed the old 2-wire style of wiring, feeding the original the transformer from limit, and adding the new Fan Center.

I have removed the old TR and re-wired as per your directions. Limit control works fine, though it's set a bit higher (220deg).

Thank you,
Dan


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## college A/C (Feb 10, 2011)

*with the furnace off*

disregard


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## yuri (Nov 29, 2008)

Glad you got it going safely.:yes:


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