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    Jeorgiagirl's Avatar
    Jeorgiagirl Posts: 7, Reputation: 2
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    #1

    Dec 4, 2005, 10:50 PM
    Gas Furnace Blows Cold Air
    This actually just started a day ago and I am trying to figure out as much as I can before calling a service person (if necessary). My apologies in advance if I am leaving out important details but I've never dealt with a faulty heater or A/C before.

    My central heater in the attic was running for about 5 hours on Sunday morning according to the thermostat log but the house was quite cold that morning. When I tried to manually get it to turn on, I could hear it make a humming noise like it usually does when it starts and about a minute later the air started blowing. Unfortunately only cold air was coming out and after a few minutes the whole system turned itself off. So being curious I climbed up into the attic, read all the warnings on the outside of the unit, and proceeded to remove a few panels and look around. I did flick the on/off switch to the off mode for the outlet connected to the unit although I imagine the main breaker was the place I really should have turned off. I did not touch anything inside since all the "explosion" warning on the outside scared me half to death. I'm glad I read all the warnings about not potentially igniting gas with flames since I had gone up carrying a lighter thinking it was the good old fashioned piloted furnace (obviously not).

    So now, after doing a few simple searches online, I am wondering if this is an ignition switch issue? Or a circuit board or fuse burned out? We were getting good heat until yesterday and now this happened. Now I'm losing sleep over how much this potentially might cost us.

    One other note, when I opened the panel in front of the fan (between the intake vent and the part leading to the burning chamber) and found what looked like a loose sheet of filter material on top of the fan. From the adhesive backing, it looks like it was supposed to be attached to the ceiling part of the chamber but had fallen on top of the what appears to be the intake side of the fan. I removed it since it looked old and dirty anyhow.

    I'd appreciate any advice or suggestions. I'll probably put out a service call this week but any insight would be great.

    Thanks!
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
     
    #2

    Dec 5, 2005, 01:54 AM
    I think you are in over your head on this one. Call for service before you hurt yourself.
    Jeorgiagirl's Avatar
    Jeorgiagirl Posts: 7, Reputation: 2
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    #3

    Dec 5, 2005, 07:04 AM
    I agree it most likely is more complicated than I can handle and I have no intention of putting myself or family in risk. But I thought I might get some idea of what is wrong from those who have more experience with this than myself.

    I generally prefer not to go into any service call (automotive, etc) completely blind. But if you think this is something far more technical than you can understand then it definitely warrants an expert.

    Thank you for your input.
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #4

    Dec 5, 2005, 07:05 AM
    I hope it is warmer where you are than here, below 10 F this morning. With all the scary warnings today, it is a wonder anybody survived before we had them all.

    Most modern furnaces follow this cycle. When the thermostat switches the power to heat, the gas ignitor comes on and heats up. Once it has had time to heat up, the gas valve opens and the combustion air blower starts. If the gas doesn't light almost immediately, the gas valve shuts off. It will try again soon if not. If it does light, the blower will come on soon, usually after a limit switch heats up, but yours must be timed. With a panel off, you could observe a cycle. You want to be able to see the burner. Locate the ignitor first. It will be a little loop or spiral of metal near where the gas comes out. Start a cycle, perhaps by pushing the switch that shuts the power off when you remove the panel. That switch is there to protect you. Do not touch any electrical terminals while holding it shut. See which step in the above sequence fails. The ignitor should get red hot, then you should hear the gas valve click open, smell gas, and the gas light. The gas valve is the box with wires between the gas pipe and the burner. If the ignitor fails to heat up, it may be bad. You can remove it and take it to a dealer for your brand of furnace and buy a new one. Before replacing it, check to see if it is getting power if you can. If it isn't getting power, replacing it won't fix the problem. Measure the resistance between its terminals if you can. If it is open, it is bad.

    If it is heating up, and the gas doesn't come on, either the gas valve is bad, or the control board is bad. Many of the problems are components on the board, tough for the DIY to find and fix. Often as not big bucks for a new board because a cheap little relay died. Circuit boards aren't that bad to replace, but I hate to tell people to replace expensive parts if they can't be sure it is the problem.

    One last thing. Do you have any other gas appliances, and are they working? The furnace will not work if it isn't getting any gas. You don't want to pay a HVAC tech to tell you that you should have called the gas company.
    Jeorgiagirl's Avatar
    Jeorgiagirl Posts: 7, Reputation: 2
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    #5

    Dec 5, 2005, 07:31 AM
    Thank you, Labman. Just the response I was looking for.

    All gas appliances throughout the house are working fine so I don't think it's the gas. I have read many of your past responses to others (very helpful I might add) but I find it odd that in my case the blower is going for about 3 or 4 minutes until it seems to figure out that is blowing cold air. Then it finally shuts itself off. In all the other examples I have read about this normally should not happen: If the ignitor does not light, it should be smart enough not to force cold air throughout the house, right? But strangely it seems to realize it is not working after a while THEN shuts itself off the blower.

    Unless I am missing something blatantly obvious and simple, I'm going to make that call although it'll probably be days until someone can come.

    Thank you.
    Jeorgiagirl's Avatar
    Jeorgiagirl Posts: 7, Reputation: 2
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    #6

    Dec 6, 2005, 09:12 AM
    Problem Resolved-Burned out Ignitor
    So service was done and turns out the ignitor was burned out. Simply its normal course of life. I checked on-line: the ignitor is about $30 plus $5 shipping. I paid over $230 for the service call (parts, labor, diagnosis) but I realize that's the price of 'expertise'. However, I intend to now always keep a new one of these things around. After turning all the power off it does not appear to be too difficult to replace the ignitor. Apparently a normal life of 2 to 4 years is not unusual.

    Thanks for your previous advice. The HVAC tech did point out some other service issues so I don't feel the visit was wasted.
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #7

    Dec 6, 2005, 10:37 AM
    If the heat is on, and you pain is limited to the wallet, you didn't do too bad. Maybe we can work you through an easier project sometime.
    James W. Acker's Avatar
    James W. Acker Posts: 17, Reputation: 3
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    #8

    Dec 14, 2005, 10:04 PM
    Hot Surface Igniter
    If you do buy an extra igniter be very careful with it. They are fragile and also never tough the carbon part of the igniter with you fingers. The oil in your fingers will shorten the life of the igniter dramaticly... Another possible problem that you may have had is your flame sensor... it looks like piece of hard wire that is in a position in front of one of the burners. If you furnace comes on and it does not detect flame it will cut your furnace off and start the cycle again... this will happen for about three times and then your furnace goes into lock down and the only thing that will run is your blower motor in your furnace. The Flame sensor can be cleaned with some some sand cloth or light sand paper. It is easier to remove the sensor to clean it.
    Jeorgiagirl's Avatar
    Jeorgiagirl Posts: 7, Reputation: 2
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    #9

    Dec 14, 2005, 11:17 PM
    Thanks, James, your advice is well taken!
    bigpoppa's Avatar
    bigpoppa Posts: 1, Reputation: 1
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    #10

    Nov 23, 2010, 03:05 PM
    Furnace keeps blowin cold air, just started,
    ga_perkins's Avatar
    ga_perkins Posts: 1, Reputation: 1
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    #11

    Dec 20, 2010, 09:24 AM
    I have a similar problem. New gas furnace sometimes blows air cold as ice. Other times it blows heat fine. I have already had the installer out once and didn't know if this is normal or not and really can't afford another bill at the momment. So, from the above statement it seems I do need to call the tech. before I freeze to death. Temp's here are in single digets and I only keep my therm. On 60 as it is. Thanks
    verelea's Avatar
    verelea Posts: 1, Reputation: 1
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    #12

    Jan 21, 2011, 09:53 AM
    My pilot light kept burning out, so I called someone to check on it. He basically flicked his lighter and said I need a new furnace. Well, $3000 later I have a new furnace that blows out cold air. I had the tech come back out and he wanted a service fee and then on top of that he wants $1000 to clean out my air ducts - this is why my air is blowing out cold is what he's saying.
    rjmart13's Avatar
    rjmart13 Posts: 1, Reputation: 1
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    #13

    Feb 7, 2011, 05:37 PM
    Do not pay that 1000.00 clean your ducts charge. That is a complete rip off and Duct cleaning is overated anyway a sell to make some money. How do I know I did it for 5 years in LI and realized this was a total waste of peoples money!
    Dikdemigaud's Avatar
    Dikdemigaud Posts: 1, Reputation: 1
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    #14

    Dec 17, 2011, 11:08 AM

    Thanks, James W. Acker!! I know your posted your response to someone some time back. But it helped me fix my furnace :) . It appears my problem was the heat sensor wire. I took it out like you said and cleaned it off with some sand paper. I put it back in and fired up the furnace. This time it stayed lit and now it blowig warm/hot air instead of cool/cold air. Before I did this the element would glow and then light the flames but within 10 seconds or so it would blow out. Now it stays lit... Woo hoo...

    Thanks again.
    zarkona's Avatar
    zarkona Posts: 2, Reputation: 1
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    #15

    Oct 19, 2012, 05:54 PM
    Sounds like u need to replace your thermocouple to me. It the air coming out is cold then it usually means your thermocouple is bad.The gas furnace thermocouple is an essential part of the gas boiler. It is 2 metal pieces that are joined at a junction, which is used to monitor the temperature of the pilot flame. This monitoring is necessary because the heat of the pilot flame sends the necessary voltage to open the valve to turn the furnace on. In order to test a gas furnace thermocouple you need to have an electrical voltage meter tester, a screwdriver, wrench, lighter, and a pair of pliers.
    Process for Testing a Gas Furnace Thermocouple
    Testing the gas furnace thermocouple entails turning off the furnace and allowing it to cool down in order to access the panel where the thermocouple is located (above the pilot flame). The voltage meter should be connected to the wires and using the pliers to hold the thermocouple, turn on the lighter in order to produce a simulated heat. The needle on the electrical voltage meter tester should move indicating that the thermocouple is operational.
    If the thermocouple passes the test, place the thermocouple back in its place and close up the panel. If it does not pass the test, replace the wires for the gas furnace thermocouple.. Hope this helps. If your technician you call doesn't test it before replacing ANY parts then he is trying to rip u off. Make sure u have him check the thermocouple before he tells u that u need any kind of part or service done.
    ma0641's Avatar
    ma0641 Posts: 15,675, Reputation: 1012
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    #16

    Oct 19, 2012, 09:10 PM
    Zarkona, note this post was originally started in 2005! Hope it is fixed now. Very few, if any, heaters today use a flame impinged thermocouple. Older ones for sure but new ones use a surface ignitor or spark. Very good detail, however, for older units
    pinkpoodles's Avatar
    pinkpoodles Posts: 1, Reputation: 1
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    #17

    Oct 28, 2012, 10:35 PM
    My Everest Extreme Comfort Furnace was installed in Nov of 2010 and I turned it on and it is blowing cold air constantly. The fan has not stopped running since I turned it on. I have the thermostat set to auto and heat and we are freezing here in WI! Should I just turn the furnace off (I see there is a switch on the side) until I can get it serviced?
    jaotsc's Avatar
    jaotsc Posts: 1, Reputation: 1
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    #18

    Nov 9, 2013, 11:13 AM
    When I set the temp higher than the current inside temp my Westinghouse furnace blower comes on and never stops until I turn it off. The air coming out is cool.

    Before the cold season began a technician changed my complicated thermostat to a simple one that my mentally disabled brother could hopefully understand. I hadn't tried the heat before that. Could that have been installed wrong? Or do you think that is coincidental. The heat worked fine last season. Thanks for your input.
    Zeugitai's Avatar
    Zeugitai Posts: 1, Reputation: 1
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    #19

    Nov 10, 2013, 06:33 AM
    Years have passed, but I'd like to extend this discussion. I have the same situation as Jeorgiagirl, the original poster. My issue, though, is that the ignitor come on and of the five burners, only the two nearest the ignitor light. It dies at this point and retries. Same thing happens. Eventually, instead of shutting down, the system winds up running endlessly blowing cold air all night, until I wake up and go down to the basement and sit with it. I start it and re-start it until it finally lights across five burners. Then it runs normally. I can't depend on it to start and run normally by itself. I have removed and cleaned the burners and the flame sensor. Same as before. I've had a HVAC tech out at no little cost. He spent all his time on the phone with someone else and finally told me he wanted $600 to $700 to install a kit that includes a new control board. I don't want to blast this furnace maker in this forum, but this unit was only four years old when this problem started. The problems are: 1) the initial lighting of the five burners. If they would light, there would be no problem. 2) when they don't light, the system should not start running all night blowing cold air.

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