Lennox Pulse seems dead

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  #1  
Old 04-07-14, 12:27 PM
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Lennox Pulse seems dead

Hi,

For the past several months, my Lennox Pulse (I think its a 1988 model) has occasionally refused to start up, so I would go to my basement, flip the power off then back on and it would fire right up and work wonderfully for a few days. I'd sometimes have to flip the power 3 or 4 times before it would start up.

I had a tech come out and he basically said we can start sinking money in it for parts or I can buy a new furnace which he highly recommended to me. Not much help eh.

Last week my little reset trick stopped working. Now the furnace will not start up no matter how many times I flip the power.

With a knowledgeable friend's help, here's the troubleshooting I've done so far:

- tested power coming into the transformer and saw 110
- tested power going out of the transformer and saw 24
- took the metal plate off and was able to spin the inducer fan no problem (doesn't seem seized)
- tested the terminals on the inducer fan for power and saw nothing
- took the ignition control module (PL605) right out and closely examined the circuit board for any burn marks, popped capacitors, or other weird stuff - all looks good to me
- removed all wires on the terminal strip and them jumped out R and W (I was told that's how to jump out the thermostat) - still didn't start the furnace
- banged my head against the cement floor a few times - furnace still didn't start

Does anyone have any ideas of what else I could try? I'm suspecting control board failure but it looked good to me. I don't know how I could test it. I've also read about a fan limit switch? Could it be that?

I hear absolutely nothing happening in the unit so its failing right off the hop.

Thanks in advance,
Dan
 
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  #2  
Old 04-07-14, 02:05 PM
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Some circuit boards have a fuse mounted. Have you checked for one and checked to see if it blew?
 
  #3  
Old 04-07-14, 02:07 PM
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Yes it does have a fuse mounted on it and it looks fine (thin wire seems intact right through the fuse).
 
  #4  
Old 04-07-14, 02:28 PM
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Hey Dan, hope your head has stopped hurting, been there. I'm not an expert on Pulse furnaces. Is there another control module in there besides the ignition module? First thing you should hear is the inducer fan. If no fan, trace the wires out and see where they go. Run it through another cylce while testing where the fan wires were.

Maybe a Pulse expert will stop by.
 
  #5  
Old 04-07-14, 02:37 PM
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Thanks skaggsje - my head is ok, thanks for asking.

I'm not sure if there is another control module or not. I don't think so, but I'm pretty green when it comes to furnace internals.

When the unit was firing up for me, I would hear the fan inducer hummm along nicely for about 30 seconds then the famous Pulse vibrating would kick on and I'd have heat. From what I've read that's the normal operation.

But now, I hear nothing whatsoever - the inducer doesn't startup at all. I've put a multimeter on the inducer fan terminals and there's no power there when a call for heat was on - mind you I had the metal plate off to do that (held on with 6 hex bolts) which I've also read is a no-no, but I don't think the unit is smart enough to detect that cover plate is off and should at least try to fire up the inducer fan.

Dan
 
  #6  
Old 04-07-14, 02:53 PM
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Dan, Take the panel off the blower section, should be the bottom panel. The module should be in there. Make sure you have 24V on R to C/
.
 
  #7  
Old 04-07-14, 03:01 PM
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Sorry I just want to clarify.

Are you saying that where the blower motor is, there should be sort of control module? I looked in there before but don't remember seeing anything other than a big fan, a motor, and whole lot of dust. I'll look again though.

Are you also suggesting that I put my two multimeter probes on R and C and check for 24V on the low voltage terminal strip in the main part of the furnace? If so, I only have R, W, Y, G, and T there.

Thanks,
Dan
 
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Old 04-07-14, 06:55 PM
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Can you post the model number. Could be like G21xx.

Strange...... I don't see a T terminal in the manual. Try checking from R to T for 24vac.
 
  #9  
Old 04-07-14, 07:08 PM
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Sure - the model number is G1403-80-C21

The "T" terminal has a black wire connected to it, in case that helps.

Thanks!
Dan
 
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Old 04-09-14, 04:22 PM
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I don't know much about pulse furnaces, but please - get that thing pressure tested before putting any money into it.
 
  #11  
Old 05-13-14, 08:25 PM
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So I bought a used ignition control module pulled from a working furnace for a good price and installed it.

I flipped the power on and voila the inducer fan fired right up! It ran for about 20 second or so followed by the usual "CLICK" but this time that wasn't followed by the usual loud vibrating hum that I'm used to. Rather this time what happened is that there was like a half a second of that loud hum sound then it stopped - almost seemed to sputter out or something. About 7 or 8 seconds after that, it seemed to have clicked off. After about another 20 or 30 seconds it seems to try again with another loud CLICK but this time nothing.

I cut power after about the 4th time the furnace tried to start up.

Now whenever I flip power on, the fan inducer starts up, then I get the CLICK about 20 seconds later, but nothing after that. It clicks off and seems to continue to try again in a cycle.

I'm guessing, based on research I've done, that it may now be the air flapper that's buggered.

Any other ideas / suggestions for what I could try?

I'm pretty close to giving up and buying a new furnace, but for the sake of DIY pleasure I'd love to see this thing fire up again.

Thanks,
Dan
 
  #12  
Old 05-14-14, 10:29 AM
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If you can interpret schematics and use a multimeter, try getting your hands on the service manual for the g14. I've seen old lennox manuals on a couple of sites.

Pulse is an unusual furnace - I wouldn't know where to start. One thing to note is that the heat exchanger in that model runs under positive pressure - so any leak is more dangerous on your furnace vs a modern model, which runs under negative pressure.
 
  #13  
Old 06-04-14, 07:11 AM
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Lennox Pulse tutorial videos

Have you watched this video series on youtube about troubleshooting a Lennox Pulse furnace? It may give you some more ideas of what the problem could be.

https://www.youtube.com/playlist?lis...otation_802004
 
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