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Old 02-08-2011, 03:02 PM   #1
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Lennox G8 reads 55volts at W


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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Old 02-08-2011, 05:33 PM   #2
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Lennox G8 reads 55volts at W


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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Old 02-08-2011, 07:46 PM   #3
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Lennox G8 reads 55volts at W


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.

:Dan
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Old 02-08-2011, 07:49 PM   #4
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Lennox G8 reads 55volts at W


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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Old 02-08-2011, 08:30 PM   #5
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Lennox G8 reads 55volts at W


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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Old 02-08-2011, 11:27 PM   #6
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Lennox G8 reads 55volts at W


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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Old 02-09-2011, 06:52 AM   #7
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Lennox G8 reads 55volts at W


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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Old 02-12-2011, 04:07 PM   #8
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Lennox G8 reads 55volts at W


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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Old 02-12-2011, 04:18 PM   #9
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Lennox G8 reads 55volts at W


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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Old 02-12-2011, 04:25 PM   #10
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Lennox G8 reads 55volts at W


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?!?

:Dan
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Old 02-12-2011, 04:45 PM   #11
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Lennox G8 reads 55volts at W


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?

:Dan
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Old 02-12-2011, 05:25 PM   #12
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Lennox G8 reads 55volts at W


Post the complete model #. Also the complete serial #. There was a G8E and other variations.
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Old 02-12-2011, 06:19 PM   #13
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Lennox G8 reads 55volts at W


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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Old 02-12-2011, 06:27 PM   #14
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Lennox G8 reads 55volts at W


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.

:Dan
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Old 02-12-2011, 06:28 PM   #15
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Lennox G8 reads 55volts at W


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!

:Dan

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