Lennox Elite Furnace won't come on


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Old 05-11-19, 11:45 AM
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Lennox Elite Furnace won't come on

First time poster with a long story.

I have a Lennox Counter Flow G24M3 75,000 BTU furnace, with a Lennox 5290 Elite II air conditioner.
This was installed in June of 1999.
The control board says 4544-E in the upper left corner.

So every once in a while the heat won't come on when called for. When it quits, neither of the two leds are lit or blinking when it's calling for heat. Both are off. The first time it quit, the service tech come out, and he "pushed on the wires going to the board" (all quotes in this post is him talking) and it started working. Well, actually the first time it quit, it started working on its own before they got here, and I called them off. So every once in a while the furnace quits for a while, then starts working on its own. The tech has been here twice, both times it starting working when he started putzing around with the wiring, without really doing anything. The second time out, he started a "you need a new control board" spiel. The furnace has quit and started working on its own at least 3 times since he said that. And of course he's talking $400-500 for a new board, "the blowers dying, that will be $600, you may as well get a new furnace" stuff.

So this last time it quit, I took the cover off, and gently pushed on the wiring. Then I did a good wiggle to the wiring to all the connectors. I went over the terminal strip with a screwdriver. I did get about a quarter turn out of each of the screws.

I did notice something while I was in there. There are two free-hanging wires coming from some sort of black plug or something above the control board. I've attached two pictures of each end of whatever it is. Both of the circled wires are hanging free (that one wire is NOT touching metal, although it looks like it), the other picture is the plug, or whatever it is. The furnace has been working fine with these two wires hanging, it's been months since the cover has been off, before I just now got in there. I have no idea where these two wires go, and I'm not messing with that.

There is power going to it. I can hear a hum, maybe a transformer type hum, go on and off when I flip the power to it. The thermostat is a mercury mechanical round one. The old standard Honeywell. The thermostat appears to be working. When I turn the thermostat down below what the thermostat says the room temp is, both lights on the board blink at the same time, about a half second on, half second off. When I turn the thermostat to call for heat, like I said, both lights go out.

Does this sould like an intermittent control board? I am comfortable with swapping the board out on my own.
Any other testing I can do. I am also comfortable with a meter.

Thanks
 
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Old 05-11-19, 02:13 PM
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It's possible that you need a new board. But first, why didn't the tech reconnect the dangling wires? Looks like they are for the blower door interlock switch. If so, what does the hot (115V) connection to the board look like? Fix the hacked stuff first before condemning anything. A larger view of your board and connections would help.
 
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Old 05-12-19, 10:56 AM
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Lennox Elite Furnace won't come on

There's one thing I didn't try before I posted yesterday. The air. It works fine.

The A/C comes on, both LED's on the board blink together when the air is going. Both LED's blink together when the thermostat is set for A/C but it's not calling for it. Both LED's blink together when the thermostat is set for Heat, but it's not calling for heat. Both LED's are out when it is calling for heat. (sorry to be repetitive from original post).

As far as the blower door switch you mentioned, the A/C is coming on when the door is off. I'm not sure what I showed in the first post is a door switch. I took a picture of the whole furnace (in the picture of the whole furnace, I put a red circle around what you may be calling the blower door switch). I do see a door switch in the schematic sticker on the side of the furnace. So I'm not sure what that's all about, since like I said I got the door off to take the pictures, and the A/C is coming on with the door off.

I included a couple of pictures of the circuit board. The LED's are not on, it's just the flash reflecting.
 
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Last edited by Pete Babacheck; 05-12-19 at 11:18 AM.
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Old 05-12-19, 11:29 AM
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To verify that the board is bad, you need to do the testing when the problem occurs.

You need to check all the inputs and outputs to/from the board with a multi-meter set to read ac volts. Sounds like the door switch is bypassed so open it and check live with caution.

Inputs to check:

1. Is the board getting line voltage - 120v consistently?
2. Is the low voltage there? -> check for 24v between terminals R and C
3. Is there a call for heat? -> Check between W and C

If all the inputs check out...

Outputs:

Is the board applying power to the inducer/vent motor? Check schematic to determine which connections supply inducer, check voltage at the board without disconnecting. (you can put the meter probs carefully into the back of wiring harnesses, you can slightly remove single terminal connections so your meter can make contact)

If the board isn't supply power to the inducer right after the call for heat begins, you have a bad board.

Only when the board detects the inducer is on via pressure switch will it energize ignitor, after a delay should energize gas valve.

---------
If the board is bad, you can change it yourself, likely under $250. At this age though, the heat exchanger should be checked.
 
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Old 05-13-19, 04:27 AM
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Lennox Elite Furnace won't come on

Thank you for the help. I wanted to mention.
All the conditions I stated in the two post I made so far, this is with the furnace not working.
It was out the last two days. When I came home last night, I intended to go thru all the checks that User 10 posted. But the furnace was working when we came home. I did nothing and it starts working.
When it dies again, I will go thru the checks you gave me, User 10.
Thanks.
 
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Old 05-14-19, 04:18 AM
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Looking at the photo in post# 3 it appears that the board may have had a burn-out on the back side of the top/left. Sure it could be from a previous board, but it would be worth popping it off and checking visually.
 
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Old 05-14-19, 07:41 AM
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Lennox Elite Furnace

Thanks Fastback.

Me and the tech are not sure what that burn mark is all about. It was already there both times he was out. He said something like "It must be from a board that was replaced in the past". I honestly don't remember any board being swapped out since I got the furnace. And that mark it's not fresh. When I had the cover off to take the first set of pictures, I ran my finger across it. It must be baked on, no smudge of any kind.

I'm thinking from the way the tech was talking, he either took it off and looked at it, or decided that the current board didn't cause that burn mark.

The next time this furnace quits, I'll take the board off myself and do what you say.
 
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Old 05-14-19, 07:34 PM
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Lately when I see those marks I've been just releasing the two white stake-offs closest to it and carefully tilt it. I then use my phone to take a photo of the board's back. The photo can be pinched out to enlarge and it eliminates the need to remove wires -most of the time-. I replaced that model board about a month ago. It wasn't cheap, OEM or aftermarket.
 
 

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