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Old 07-30-2009, 09:57 PM   #1
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Need help getting just the fan to run on a Lennox Elite


Hi,

I live in the Pacific Northwest where we rarely have a need for AC (last few days not withstanding). I have a Lennox Elite gas forced-air furnace, and I'd love to be able to run *just* the fan on this unit during the hot days so we can get some cooler air from our basement flowing through the house.

I've played with the thermostat to try to get just the fan to come on, but nothing I do on the thermostat works. I've also poked around the furnace itself to see if there was a "fan-only" switch or something else similar, but didn't find anything.

So I'm guessing that perhaps either a) the Lennox Elite doesn't support fan-only operation (which seems odd), or b) the installers didn't hook up the Elite and the thermostat correctly.

Does anyone know how I can get just the fan to run on this unit?

Thanks!

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Old 07-31-2009, 07:58 AM   #2
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Need help getting just the fan to run on a Lennox Elite


Need more info. What kind of thermostat do you have. is it a heat only or are there switches for an A/C? How many thermostat wires are there?

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Old 07-31-2009, 08:10 AM   #3
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Need help getting just the fan to run on a Lennox Elite


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Need more info. What kind of thermostat do you have. is it a heat only or are there switches for an A/C? How many thermostat wires are there?
I can't recall the model, but it's a programmable thermostat with options for setting to "heat", "cool", and "off". So I'm fairly confident it's capable of cooling if I had AC. Also, when I looked at the furnace itself, there were only 2 or 3 wires coming from the thermostat actually hooked up to the control board on the furnace (red, green, and perhaps one other color were attached, while a blue and yellow wire were unused and left dangling). I'm out of town for work right now, so I can't check, but that's what I recall.
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Old 07-31-2009, 09:33 AM   #4
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Need help getting just the fan to run on a Lennox Elite


Post the model and serial # and I will figure it out for you.
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Old 08-01-2009, 04:48 PM   #5
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Need help getting just the fan to run on a Lennox Elite


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Post the model and serial # and I will figure it out for you.
Thermostat is a Honeywell TH4110B 1009.
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Old 08-01-2009, 04:52 PM   #6
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Need help getting just the fan to run on a Lennox Elite


Model and serial # of the furnace. I am a Lennox tech.
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Old 08-01-2009, 04:59 PM   #7
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Model and serial # of the furnace. I am a Lennox tech.
Ahh, sorry - here it is.

model G61MP-48C-090-06

serial 5905E05029
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Old 08-01-2009, 05:51 PM   #8
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Need help getting just the fan to run on a Lennox Elite


Thats an easy one. If you have 3 wires or 4 going to the thermostat hook R on the board to R on tstat. W to W and G to G. Unit then works with fan in ON position. If you only have 2 wires then you can cheat: Get a toggle switch and mount it to the side of the furnace and run a wire from R on the board to one side of the switch. Run a wire from G to the other side of the switch. This is 24 volt wiring and use a minimum #18 wire. Very good furnace but it needs some annual maintenance. Get a experienced Lennox tech to clean the flame sensor and check the ports on the collector box where the pressure switch tubing attaches for sulphur buildup in the ports. Flame sensor is VERY difficult to get at and NOT a DIY project. I usually remove the top of the burner box etc and clean it and the face of the burner it sits in front of with emory paper. Failure to do this maintenance will get you flame failure lockout. That is a 2 stage furnace and may have wires on W1 and W2. If so you need a 2 stage thermostat and wire it accordingly.

Last edited by yuri; 08-01-2009 at 05:55 PM.
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Old 08-01-2009, 06:24 PM   #9
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Need help getting just the fan to run on a Lennox Elite


Thanks, Yuri. It is a two stage furnace, if I recall correctly from when we had it installed. And thanks for the tips on maintenance - it's on my list to do in the fall this year.

From the thermostat to the board, the R connects to R, G to G, and the W on the thermostat connects as follows:

- W from the thermostat attaches to a blue wire that goes into what appears to be the condensation pump.
- Then a blue wire comes out of the condensation pump, and connects to W1 on the board.
- Then a red wire connects from W1 on the board to W2 on the board.

And when I turn the fan to "on" on the thermostat, nothing happens. Do you think that the thermostat is incompatible with the Lennox control board because the Lennox is 2-stage and the thermostat is not?
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Old 08-01-2009, 06:29 PM   #10
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Need help getting just the fan to run on a Lennox Elite


BTW. the thermostat has wires as follows:

W, Y, G, O, Rc, R, B, C

And as I indicated, only the W, G and R are wired up.
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Old 08-01-2009, 06:34 PM   #11
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Need help getting just the fan to run on a Lennox Elite


It should work the way you have it. You may have a faulty thermostat or bad wire connection at G or the G at the board. The blue wire is to a safety switch on the pump in case it fails. The jumper between W1 and W2 is okay. You still have a 2 stage unit and a timer switches stages. Check for 24 volts between R and C on the board with the door switch pressed in. There usually is a minibreaker on the side of the electrical box the board mounts on or a fuse on the board. You may have shorted something/tripped it. If all else fails get the Lennox tech out early, have the maintenance done and he can help you and you save one service trip charge.
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Old 08-01-2009, 06:36 PM   #12
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Need help getting just the fan to run on a Lennox Elite


Oops, I got the thermostat capabilities wrong. My thermostat actually has:

W, Y, G, O, Rc, R, B
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Old 08-01-2009, 06:37 PM   #13
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Look up one post for more info.
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Old 08-01-2009, 06:42 PM   #14
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Great - thanks, Yuri - I'll check it out.
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Old 08-01-2009, 07:22 PM   #15
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Ok, making some progress here. First off, there are 24 volts (if I read my multimeter correctly) when hooked up to R and C with the door switch pushed closed. Secondly, I discovered that if I have the thermostat set to "Heat" with the fan setting to "On", then I get some reaction from the furnace - there is a short "click", then a steady humming sound, and the DS1 and DS2 lights on the furnace board are flashing in unison, about once every second. Fan still doesn't kick on.

I found the mini breaker on the side of the board (looks like a little toggle switch, and says "3 amps" on the side?).

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