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    Brad J.'s Avatar
    Brad J. Posts: 1, Reputation: 1
    New Member

    Oct 31, 2005, 11:37 PM
    Blower fan works in A/C but not heat
    A couple of weeks ago my Lennox G20Q3E-75-1 was acting up. Gas valve was cycling when calling for heat and then once satisfied and the main burners went out the pilot light was staying lit. I thought it might be the flame sensor as far as the gas valve cycling and didn't want to tear into it so I had a tech come out. He removed the sensor, cleaned it and reinstalled. Worked almost OK but the pilot was still staying lit. The pilot should go out the same time the gas valve shuts down on this unit because of the electronic iginition - yes? Determined that the gas valve was sticking so I gave it a tap and pilot went out and the problem hasn't reoccurred since then. Now this morning the blower motor will not cycle on after the burners are on for a short time. I think it high temp limits out and then shuts down the gas valve. I can hear and feel the relay on the circuit board clicking but don't know if power is getting transferred to the blower motor from the relay or not. Blower does not work in either auto or continuous fan mode. I switched from heat to A/C, lowered the temp so the A/C would come on and the blower comes on normal in both auto and continuous fan mode. Is the relay for the heat cycle on a different relay than the A/C which is causing the problem or should I try and change the blower speed wiring to see if that would work. Don't want to burn out a board if I miswire something or what else could be wrong? Any help would be appreciated!
    fredg's Avatar
    fredg Posts: 4,926, Reputation: 674
    Ultra Member

    Nov 1, 2005, 05:12 AM
    I would call the same repair person again, give that person one more chance to find the problem. If he/she doesn't, then call a different repair person. A friend recently had the same type of issues, cost around $133 for the repair... works fine now. She "got lucky", with the repair person being one of many yrs experience, and found it right away.
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
    Uber Member

    Nov 1, 2005, 07:52 AM
    I think you have it largely figured out. Different brands of furnaces may do things differently. There are 2 limit switches. The lower temperature one closes allowing the blower to start once the gas has warmed the air inside the furnace. The upper one shuts the gas off if it overheats because the blower didn't start. The furnace uses a separate relay and a separate blower motor coil allowing a lower blower speed in heat than fan or A/C. You need to check the low temperature limit switch. It is in the heat exchanger area where it is heated by the gas, and cooled by the air flow. It may just need cleaned the same as the flame sensor. If you clean it up and it is closing after the gas comes on, the last thing to check would be the blower coil. Try to identify the lead from the heat relay to it. Unplug it and jumper it to the power feed from the house. Remember 120 volts can kill. If the blower then runs, the board is bad. Few of us can do like the guy posted last night. He took the board out, took it to work, found a bad 25 cent capacitor, replaced it and it worked fine. I paid $300 for a new board for my furnace when it was largely doing the same as yours.

    Look back through the questions here. The relays on the board are usually the problem, but few choose to try to fix them. The older furnaces with separate relays were much easier to fix. Once you are sure the blower works, the limit switch works, you may as well save the service call and replace the board yourself.

    Ignore Fred. He posts poor answers in a number of areas he knows little about. What his vet does for his dog, could kill other dogs. He has been kicked off several sites for causing trouble.
    ForumCrawler's Avatar
    ForumCrawler Posts: 3, Reputation: 1
    New Member

    Dec 25, 2005, 05:23 PM
    Same problem but it is Honeywell. What should I do?
    Hi Labman,

    I just got the same problem as Brad, except mine is Honeywell with 2 zones. I went to attic and checked out the system: when I turned on zone one (or two) with AC or FAN, they worked OK as expected. But when I turned on HEAT, the lights indicated correctly and the system turned on and run, then I heard some kind of sizzling sound (like gas coming out) then it runs for 1 minute and turned off without any air blowing out. I tried to unplug and also press the BOOT button but it did the same thing. The first time I did it, it seemed to work OK with heat blowing out but since then it never worked again. What should I need to do to have the heat turn on again? Probably, the gas was not burnt because it was not lit (like the water heater) or something, if so where do I need to light it? Does it have any pilot light somewhere I need to light or ignition switch somewhere I can clean up? Do I need to clean up something? Please help. We did not have heat for several nights now... It really worries me because when the unit runs for 1 minute and stops, I smell some gas. Any help would be appreciated. It is 2 year-old gas central-heat system.

    Thank you very much in advance.
    wheatnbarley24's Avatar
    wheatnbarley24 Posts: 63, Reputation: 3
    Junior Member

    Dec 25, 2005, 07:54 PM
    Brad js problem is more than likely a bad control board. I would have a technician diagnose the problem then with the model and serial number locate a new board and change it yourself. Save a few bucks
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
    Uber Member

    Dec 25, 2005, 08:04 PM
    Your system may work much like mine. When the thermostat calls for heat, the small blower for the draft comes on, then the ignitor, and then the gas. The blower then comes on after a timed delay. If the blower doesn't come on, the gas will shut off. If anything fails to start, it will shut down and then start from the beginning. Some furnaces use a temperature limit switch to start the blower instead of a timer. What you need to do is to determine which steps are successful, and then check the next step. If the gas starts burning, but the blower doesn't start, you should be able to feel the vent heat up. If the gas doesn't ignite at all, it may be fairly cheap and easy to replace the ignitor. It is a little loop or spiral of metal with 2 wires near where the gas comes out.

    Otherwise, whatever the problem is, likely it is on the circuit board. It is very hard to find and fix problems on the board. The boards are not too bad to change, but expensive $100+.

    Note, if the system is only 2 years old, it may still be under warranty.
    ForumCrawler's Avatar
    ForumCrawler Posts: 3, Reputation: 1
    New Member

    Dec 25, 2005, 08:55 PM
    Thank you wheatnbarley24 & Labman for quick response.

    I wouldn't mind if I get my hands dirty. By the way, I love to learn to fix things and do it myself.
    To get started, how/where do I check for the pilot light in my furnace (or the ignitor as you mentioned)? Do you have a diagrams, picture or instructions on how to replace it? I believed probably it was the ignitor/pilot light problem because as I mentioned earlier, the first time when I rebooted the board I felt the vent (connected from one side of the furnace to the top of the roof to outside) was hot. After I turned it off and turned it on again, it never got hot again and the only thing I heard was like it was running but just for 1 minute or so then it turned off without air blowing and never turned on again until I restart it. But I would take your suggestions: I will contact Honeywell tomorrow and ask if it is still under warrantee. The problem is, I don't know which model it is. Can you help? Meanwhile, I had to purchase some heater for my Mom and sister but I have been really freezing... It is XMas' cold silent nights, that is! :p Still have some hopes...

    Thank you very much in advance.
    FC ;)
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
    Uber Member

    Dec 25, 2005, 11:06 PM
    Usually there is a decal with some instructions on the unit somewhere that includes the model number. Most newer units use a ignitor that get hot enough to set the gas on fire rather than a pilot. It sticks into the path near where the gas comes out of the gas valve. Can't direct you to a diagram.
    ForumCrawler's Avatar
    ForumCrawler Posts: 3, Reputation: 1
    New Member

    Dec 26, 2005, 11:02 AM
    Thank you
    Thank you Labman. I had only the wiring diagram/instruction they left in the attic when I moved in. Did not have anything else :o . I will try to contact Honeywell today to see how it goes. I wish I could get some kind of user manual or some sort like the water heater did.

    Again, thank you.

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