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| Moderated by: RegUS_PatOff, hvacdrd, applianceman18007260692 |
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| Lennox Pulse Furnace | Rate Topic |
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| Posted: Mon Oct 9th, 2006 04:21 am |
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1st Post |
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Crouching Tiger Sublime Master of Appliantology
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Fired up the furnace 2 weeks ago and everything was running good until three days ago when the unit came on for about 30-45 seconds and than shut off. I called for heat about 3 hours later and the unit came on and ran ok with no problems. The next day a call for heat was needed and the furnace came on and then shut off after about 45 seconds but the blower remained on while the furnace made a second attempt to start which was successful. The third day the furnace came on and then repeated the same problem as before - on for about 45 seconds then shut off, except for the blower, and then re-started and stayed on for the complete cycle. I decide it was time to check it over. I have 24 VAC between R and C and C and W when calling for heat. I also have 24 VAC at the gas valve after pre-purge and the diff. pressure switch is closing. I did find and repair a leak in the exhaust tubing where the diff. pressure switch hose connects to the 90' fitting on the tube. I restarted the unit and it shut off only once after making and breaking the cycle about three times. My temp rise is also good from 70'F - 135'F before the blower comes on. The factory blower setting is 45 sec. on and 180 sec. off. I have not yet checked the gas pressure or the spark plug to see if I have good spark. The air diaphragm has not been replaced in 10 years and the manufacturer states that it should be replaced every four years regardless of condition so I think I will do that as well. I have also looked at the vent termination and it is ok according to manufacturers install instructions. Any suggestions or info reagarding this problem would be appreciated.
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| You have chosen to ignore ahammer48. click Here to view this post |
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| Posted: Tue Oct 10th, 2006 02:32 am |
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3rd Post |
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Crouching Tiger Sublime Master of Appliantology
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Thank-you for your response in regards to my Pulse problem. However there is no spark ignitor or gas burner in this unit, it is an actual spark plug like an internal combustion chamber. The term Pulse comes from the combustion process where gas and air mix in the combustion chamber. A spark ignites the initial combustion - this is the first pulse. Pressure then forces combustion products to travel down the tailpipe. Air and gas re-enter the combustion chamber as the exhaust gases leave the chamber. A new mixture is ignited and continues the cycle to 60 pulses every second. When the furnace starts you can hear the pulse process taking place. Then the unit dies out after 45 seconds but the blower will remain on and than the furnace will begin the pulse process again and stays on for the rest of the cycle. I have tried the unit again today after fixing the leak at the diff. pressure switch tubing and it ran without a problem. However I did not keep it on for more than 5-6 minutes because it was already 74' F inside the house. I hope this will provide a little more background at how the system operates and the problem at hand. Again thank - you for the help.
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| Posted: Tue Oct 10th, 2006 10:31 pm |
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4th Post |
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hvacdrd Fellow, Academy of Sublime Masters of Appliantology 
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After start up listen for a change in sound before it shuts down and retries ignition. If it sounds like it is bogging down verify that no exhaust gases are recirculating. If there is not a noticable noise change check in this order 1 - verify that the pressure differential switch stays closed - if it opens the likely cause is a blocked condensate line, or partial blockage of the air intake pipe (ie - wasp nest in pipe) 2 - Check & monitor flame signal - Normal signals are: Watsco Primary Control - 3 to 5 microamps DC Gas Energy Primary Control - 25 to 35 microamps DC Lennox GC-1 Primary Control - 18 to 35 microamps DC Since this is a Pulse furnace you may not get a steady reading, if your meter has an averaging feature it helps. The most common problems I have had on these units are blocked condensate lines, exhaust recirculating into the intake, and Primary Control failures. Normal manifold pressures are 2.0" w.c. for natural and 9.0" w.c. for LP Normal exhaust temps are 110-125F - should not exceed 130F You are correct on the Air Flapper material replacement every 4 years per Lennox but I know of several that have never been changed. Hope this helps
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| Posted: Wed Oct 11th, 2006 01:23 am |
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5th Post |
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Crouching Tiger Sublime Master of Appliantology
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Thanks for the new information hvacdrd. I checked the condensate line which runs into my sump hole and it appears to be normal, I will still check it at the tee fitting for any partial blockages. As stated in my initial post about the leakage at the diff. pressure hose, is it possible that this was the primary problem? I did not state originally that we had a problem about 6-7 years ago where the furnace would shut off even before the blower would come on and it would happen until the unit locked out. That was when we had insurance through Union Energy and their technician changed the primary control and some other parts that did not fix the problem. Finally Union sent out another tech. from a local heating company. He came and looked it over and found that the exhaust and intake were installed wrong and, under the right weather conditions, was causing the exhaust to be recirculated and stop combustion. About a month later we received a notice that Union Energy was cancelling our insurance because the furnace was a high risk maintenance issue. But after that one and only problem the furnace has run good until now. Let me know what you think about the leak problem.
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| Posted: Wed Oct 11th, 2006 02:01 am |
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6th Post |
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hvacdrd Fellow, Academy of Sublime Masters of Appliantology
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Odd thing about the pressure differential switch on the Pulse. The contacts are normally closed and only open if there is a problem. Most units use the switch in a normally open state and close to prove that the inducer is running. Always seemed backwards to me but it works. If there is any question if this is the problem you could wire a low amp fuse(1/100a) in parallel with the contacts, if the fuse blows at any time then you know the switch opened at some point. Keep me posted and I'll try to dig up some other information if you need.
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| Posted: Sun Oct 29th, 2006 01:15 pm |
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7th Post |
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jjrudyjr Grasshopper
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I had the same condition last fall with my G21 pulse. The condensate line appeared to be o.k. (water coming out of tubing) But the bottom of the drip leg on my unit was plugged with rust and sediment to the point that the furnace was producing more condensate than the pipe could discharge. I cut the cap off of the end of the pipe and cleaned it out and put a rubber Fernco cap on it with a stainless clamp. I had my original Pulse replaced with the G21 under warranty and nobody ever checked for this condition in the 20 plus years I have had a Pulse furnace. Hope this helps.
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| Posted: Sun Feb 4th, 2007 03:34 am |
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8th Post |
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Crouching Tiger Sublime Master of Appliantology
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I forgot to post back about my furnace issue. I broke down and called a local service company to see what was goin' on. He checked and adjusted the gas pressure and talked about the possibility of the condensate line being plugged and a few other things. In the end he really didn't do a goddam thing but charge me 100 bucks for the call. So I check the drain line which had a removable plug and I cleaned out some junk but the problem still went on. Then I kept on focusing when the unit shut off - before the blower came on - like it was tripping on the hi-limit. So I sit in front of the damn thing for about an hour with my amp probe on the blower and finally 9-10 amps on the motor. The start cap. was no good! Duh! So I slam another cap. on it and she runs like a dream. Thanks for all your suggestions guys.
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| Posted: Mon Feb 5th, 2007 05:42 am |
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9th Post |
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That Guy Sublime Master of Appliantology 
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Change out the air diaphragm if you haven't already. They get kind of rotten after a while. The pluse is kind of like a one cylinder engine and the air diaphram is its valve. Its a pretty important part.
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| Posted: Wed Feb 7th, 2007 03:08 pm |
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10th Post |
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AYUDANTE Senior Apprentice Appliantologist
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I concur with ahammer48. in my experiences i find the flame sensor being dirty or just needing replacement. replacement is easy, just remember to disconnect unit before doing any electrical work. ayudante.
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| Posted: Thu Feb 8th, 2007 01:05 am |
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11th Post |
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Crouching Tiger Sublime Master of Appliantology
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Perhaps I was not clear on my last post. The blower motor start capacitor had failed causing the delayed start in the blower which would then trip the hi limit thermostat within approx. 45 seconds. Everything else with the unit is good - diaphragm, sensor etc. I replaced the start capacitor about 3 months ago and I haven's had a problem since.
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