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Old 12-05-2009, 12:27 AM   #1
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Lennox 80MGF gas furnace question


I have a Lennox 80MGF2-60A-5 gas furnace. It was installed in October of 1996.

It was having problems firing when a heating demand was called for. An HVAC company diagnosed it needed a new circuit board. They wanted over $400 for a new circuit board/labor. I bought one for $135 and installed it myself.

I replaced the existing original EGC-2 circuit board (28K62) with 17W82 (ignition control conversion kit LB-91097C), which is an EGC-1 board myself. Heating works great now!

One little issue I'm hoping someone can help me with. Everything works except my Fan when set to continuous 'on'. Again, the unit works smooth when a heat demand is being called for by the thermostat, but when I turn the Fan to 'on' instead of 'auto' (just trying to have the fan continuous "on", no heating demand), I hear a click from the unit and nothing happens. No diagnostics on the LED's either.

When I replaced the circuit board I marked all wires and made sure they all went to the appropriate place on the new circuit board.

My thermostat does have a green wire that went to the old G terminal on the original circuit board. I hooked the green wire to the G terminal on the new circuit board as it had been on the old board.

Any ideas why the continuous fan will not operate and I just hear a 'click'? As I said, the heating cycle works beautifully, just when I set the fan to "on" instead of "auto", nothing happens but that 'click' noise!.

The fan worked when set to "on" before with the old circuit board.

Thanks.

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Old 12-05-2009, 01:26 AM   #2
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Lennox 80MGF gas furnace question


I've seen that before.
There should be a fan terminal between Heat and Cool. Most boards label it continuous, but Lennox labeled it Low. Connect an unused fan speed wire to it.


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Old 12-05-2009, 02:15 AM   #3
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Lennox 80MGF gas furnace question


Thanks for the quick reply! I'm attaching a diagram of my ECB-1 board. It looks different than your posting but that may not matter. The new circuit board came with a "continuous fan jumper", but I didn't install it. (My old EGC-2 board didn't have a terminal for ACB LOW)

I read the instructions below that came with the new circuit board and may have misinterpreted. These are directions for replacing an EGC-2 with the new part, an EGC-1 board, which is what I did.

Blower Speed and Continuous Fan Connections: Existing units with continuous low speed fan operation: Do not install provided continuous fan jumper as shown in figure 1 and do not change existing low speed tap connection. Make the ACB HEAT and ACB COOL connections as shown.

Existing units with no continuous low speed fan operation: Connect provided continuous fan jumper between control board terminals ACB HEAT and ACB LOW to obtain continuous fan operation on the heating speed when thermostat is set toFAN ON and there is no heating or cooling demand. Make the ACB HEAT and ACB COOL connections as shown in figure 1. ***Warning - Do not install jumper if continuous low speed is installed, either at control board ACB LOW terminal or to aseparate circuit controlled by terminal G of the thermostat. Damage to the control board andlor blower motor may result.

My original EGC-2 board did NOT have a terminal for ACB LOW. But, it did have a thermostat wire hooked to the G terminal on the board. So when I made the new board connections I thought since I had an existing thermostat wire G terminal connection, the 'warning' above in the instructions applied to me.

Did I misinterpret possibly and need to use the continuous fan jumper? Here I have the heat working now, but don't want to cause damage to the control board if I use the jumper that came with the replacement kit.
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Old 12-05-2009, 07:53 AM   #4
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Lennox 80MGF gas furnace question


The old board energized the cooling fan speed relay when set to ON. You DON"T use the jumper. Take the red unused wire from your fan motor and hook it to the ACB Low terminal. Yellow or Blue to heat and Black to cool. If you bought the board from Cozy then phone them. They have tech support.
http://tech.lennoxintl.com/PDFs/9801b.pdf
Check page 32:
Low goes to the ACB Low.
Save that pdf file/manual to your computer for future needs/reference.

Last edited by yuri; 12-05-2009 at 08:06 AM.
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Old 12-05-2009, 12:37 PM   #5
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Lennox 80MGF gas furnace question


Quote:
Originally Posted by yuri View Post
The old board energized the cooling fan speed relay when set to ON. You DON"T use the jumper. Take the red unused wire from your fan motor and hook it to the ACB Low terminal. Yellow or Blue to heat and Black to cool. If you bought the board from Cozy then phone them. They have tech support.
http://tech.lennoxintl.com/PDFs/9801b.pdf
Check page 32:
Low goes to the ACB Low.
Save that pdf file/manual to your computer for future needs/reference.
My old board is the EGC-2 in the manual you posted, thanks, I did save it for reference! It does not have an ACB LOW terminal on it.

Ok, I didn't use the jumper due to the warning. I'll look in the furnace for an unused wire from the fan motor. I didn't notice any unused wires when changing out the board. It may not be there because it was an EGC-2 model which didn't have the ACB LOW terminal?
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Old 12-05-2009, 01:17 PM   #6
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Lennox 80MGF gas furnace question


Look carefully at the motor to see if it has more wires coming from it ie:red. Some Lennox motors have a jack terminal built onto the motor with spade terminals which you can add an extra wire to to create the low speed wire. HOWEVER that jack can break EASILY and short out the motor, blow the new board and do LOTS of damage. They discontinued it for that reason. I would leave it ALONE.
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Old 12-05-2009, 04:39 PM   #7
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Quote:
Originally Posted by yuri View Post
Look carefully at the motor to see if it has more wires coming from it ie:red. Some Lennox motors have a jack terminal built onto the motor with spade terminals which you can add an extra wire to to create the low speed wire. HOWEVER that jack can break EASILY and short out the motor, blow the new board and do LOTS of damage. They discontinued it for that reason. I would leave it ALONE.
I think I will do that, leave it alone! Everything works. I can live without the fan having the ability to run continuous. I've lived in this house for 11 years and never once just ran the fan. It's always run as "auto" with a heating or cooling demand.

If you have time, help me understand something. The old EGC-2 circuit board did not have an ACB LOW terminal. There doesn't appear to be an open jack terminal on the motor that I can see. The fan would run continuous when set to "on" with this old circuit board. I assume the G terminal for the green thermostat wire controlled that function, calling for "on" when it was set that way on the thermostat.

So now I have a new circuit board, an EGC-1, that does have an ACB LOW terminal, but I don't have a wire to put to it. And as I said, no visible jack on the motor to run a wire to it. How was the fan controlled with the old circuit board if there is no wire running to it? A separate circuit?

The new circuit board came with a continuous fan jumper that can be run from the ACB HEAT terminal to the ACB LOW terminal, but as I posted, the warning message in the instructions makes me think I shouldn't do that.

Thank you both for commenting on my thread. I'm good to go and have heat, I just hate leaving the "on" function of the Fan not working, even though I never used it for 11 years...haha.
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Old 12-05-2009, 04:54 PM   #8
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Lennox 80MGF gas furnace question


The old board energized the cooling speed with a call for continious blower. The new one energizes the "low" terminal for continous blower. The jumper takes the power from low and feeds it to the heating speed in continous. Some of the motors, like yours, only had two wires plus a neutral so the jumper is needed for continous to work. Jumper low to heating speed is fine, jumper cooling speed to heating speed and you'll let the smoke out.
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Old 12-05-2009, 05:38 PM   #9
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Quote:
Originally Posted by Marty S. View Post
The old board energized the cooling speed with a call for continious blower. The new one energizes the "low" terminal for continous blower. The jumper takes the power from low and feeds it to the heating speed in continous. Some of the motors, like yours, only had two wires plus a neutral so the jumper is needed for continous to work. Jumper low to heating speed is fine, jumper cooling speed to heating speed and you'll let the smoke out.
So going back to my original post...currently when I turn the thermostat to Fan "on", all I hear is a click noise. That is because the G wire on the thermostat is hooked to the G terminal on the circuit board, however there is no power going to the Fan itself for this signal to activate.

If I put the "continuous on jumper" from the ACB HEAT to the ACB LOW, then that same signal from the thermostat to the G terminal will activate the fan in "on" and the power comes from the voltage that is jumpered from the ACB HEAT terminal thus energizing the motor on the blow to just blow air w/o heat or cool?

I would love to just use the jumper and see what happens...jumper from ACB HEAT to ACB LOW and try it..but I'm afraid if that isn't it I'll damage the board or the fan motor.
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Old 12-05-2009, 05:58 PM   #10
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Lennox 80MGF gas furnace question


You'll be fine using the jumper. If you had a wire hooked to heat, one to cool and one on low then the jumper would power up two speeds at the same time causing damage. With no wire on low it can only energize one motor lead at a time so there will be no damage.
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Old 12-05-2009, 06:01 PM   #11
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FYI it costs at least $1 /day to run that fan. That is why newer units have an energy saving ECM motor (80 watts instead of 360 watts). If the motor is replaced with a 3 or 4 speed motor wire it the way I said and it will be fine.

Last edited by yuri; 12-05-2009 at 06:03 PM.
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Old 12-05-2009, 07:10 PM   #12
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How many wires do you have from your fan motor. What color are they and where did you put them on the new board. The black wire from the motor should be on acb cool, the brown wire from the motor should be on acb heat and the red wire from the motor should be on acb low. All the rest shoul be on park except the neutral (white). Let me know if you do not have a brown
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Old 12-05-2009, 10:18 PM   #13
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Lennox 80MGF gas furnace question


My fan motor wires are black for ACB cold and red for ACB hot, and the old EGC - 2 board didn't even have an ACB low terminal for a wire to be run to it from the fan. (see attached picture. Hard to see, but at the top, middle of the board are the red and black wires..this is a picture of the old board before I replaced it.)

When I put in the new EGC - 1 board, I made sure to put each wire in the same labelled spot on the new board as the old. I carefully marked each wire prior to removal and numbered them and wrote the numbers on the schematic in the manual that came with the new board.

I ended up running the 'continuous on jumper' from ACB hot to the ACB low and the fan now works when the thermostat is set to fan "on" (no demand for heat or cold, just fan to "on")

I'm all set, thank you all for your replies! I made a big deal about the fan running 'continuous on', which I never ran just the fan only, but I wanted it to work like it should and have that ability or I wouldn't have felt like my DIY circuit board replacement had been successful!

Thanks again,

Pdxsk
Warm in Seattle again!
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Last edited by pdxsk; 12-05-2009 at 10:21 PM.
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Old 12-05-2009, 10:22 PM   #14
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Alls well that ends well. Now we don't have to call you "Sleepless in Seattle" wondering about your low speed.
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Old 04-01-2011, 12:23 PM   #15
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Lennox 80MGF gas furnace question


I have problem with heating during My furnace operation...

Start from begainning...

1. combuston air blower starts
2. after 15 sec(~) flame starts... and just within 2-3 second flame stops..(this is the problem)
3. again after another 15 sec~ flame starts and it stops within 2-3 secs... but not countinous flame runs till call for Air Blower to starts... cycle interept in between? and no any error code show by led ( shows Heat Mode On)

This problem will fixed .. if i shut off main power for 2 min. and start again. but i cant not do every one hour when furnace starts to match up setting for heat.. Hope you understand..

Now Guide me what is the problem? and why its doing like that? and what should i do? Thanks

Furnace details
LENNOX (14 YRS OLD)
Heating Units - Gas DSI
80MGF

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Last edited by yyzcctb; 04-01-2011 at 12:32 PM.
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