Home heating / furnace help

Hi
I know nothing about furnaces but something about the way my furnace works doesnt makes sense to me and I was wondering if someone could give me an explanation...
I have a Carrier Weathermaker 8000 58WAV furnace. It blows air continuously. From visual inspection it looks like it draws air from the basement. It cycles between warm and cool air. The problem is where I live in the winter it gets extremely cold(can get as cold as minus 40 degrees). The house is very old and the basement is very cold. So the furnace cycles between very warm and very cold air which is very uncomfortable and I can't imagine it being very efficient. Is this a normal setup for a furnace? This is my 1st home and Ive only lived here for 1 winter so I know very little about this stuff. I remember my parents furnace didnt blow air continously. It only blew air on the warm cycle. That seems to make much more sense to me than cycling between very cold and warm air.
Thanks in advance for any insight
Dennis
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On Sat, 9 Feb 2008 21:35:21 -0800 (PST), snipped-for-privacy@gmail.com wrote:

You need to watch what the furnace does. Sounds like it's cycling on the high limit switch (meaning the burners fire, the system over heats, the burners goe off on the limit switch, the blower stays on, the furnace cools of, the furnace fires, repeat cycle.). make sure you filter is clean and ALL of your vents are open.
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Furnace Guy wrote:

Hi, Or simply filter could be so dirty it is restricting air flow tripping high limit sensor.
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Hi Tony
The filter is new.
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On Feb 9, 10:56 pm, Furnace Guy wrote:

Thanks for the quick reply!
I think the furnace is operating properly. Maybe I wasnt specific enough about its operation.
If the house is warm the furnace blows cool air. Once the temperature drops below the set thermostat level the blower stops for a short time(seconds). Then the furnace ignites. Then blower comes back on and blows warm air until the house is heated. It was my limited understanding that this is how newer furnaces work. They have a continous airflow(well almost continous..theres a short break just before ignition). This makes sense to me for summer operation. The house can be somewhat cooled by drawing cool air from the basement and circulating it. It doesnt make sense in the winter.
The filter is new. I replace it every few months.
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On Sat, 9 Feb 2008 22:22:01 -0800 (PST), snipped-for-privacy@gmail.com wrote:

That is NOT how a furnace works. With the thermostat fan switch (which you don't have) set to auto it goes like this:
Call for heat, inducer motor comes on, pressure switch makes, limit switche checked and if closed then ignition happens, burners fire and aprox 90 seconds later the indoor blower comes on. Once the thermostat is satisfied the burners go off and the indoor blower goes off aprox 90 seconds later. If your indoor blower is staying on when there is no call for heat AND the thermostat setting has been met then you have a bad fan limit switch if your furnace is older or a bad fan relay.

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On Feb 9, 10:35 pm, snipped-for-privacy@gmail.com wrote:

After doing some digging around it would seem that some furnaces have two modes...Fan "On" and "Auto". Theres no mention of it in the furnace manual but Im starting to suspect my furnace has this option that can be set from the thermostat. The problem is my thermostat is one of those old kind with the mercury tube in it. No fan settings. Maybe the previous owner upgraded the furnace but not the thermostat. There's only two wires travelling from the furnace to the thermostat so even if I had a newer thermostat with a fan setting, there arent an fan wires to connect it too. Is it possible my furnace is stuck in "ON" mode?
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On Feb 10, 2:30 am, snipped-for-privacy@gmail.com wrote:

That' what it sounds like. Normally, there is a switch setting on the thermostat to set the blower to either auto or on. Since your thermostat only has two wires and no such switch, it sounds like the furnace itself is wired for the blower to be on all the time. Personally, I would not want it set up that way. Most are set for the blower to come on only when heat is being delivered. With an older furnace and conventional blower, this is going to consume a lot of electricity. Newer high efficiency blowers it would use a lot less, but still will add up run 24/7.
Regarding sucking air from the basement, what makes you think it's set up that way? There should be return ducts going to the living space that bring that air to the suction side of the blower.
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On Feb 10, 7:27 am, snipped-for-privacy@optonline.net wrote:

So it turns out I was on the right track. There's terminals in the furnace for fan operation that weren't being used(my thermostat is only 2 wire) I learned of these terminals from an online post about a different brand of furnace but figured it was a standard setup. I wired up the fan terminals to a manual switch and now my fan only comes on during the warm cycle!! So Im pretty happy about that.
As for air being sucked in from the basement. Theres a return duct in the basement that eventually leads to the filter and then blower chamber. This makes great sense for house cooling in the summer but makes no sense in the winter. To me it would make more sense if there was a 2nd return duct upstairs where the air is warmer. With that setup one could close the downstairs duct in the winter and open the upstairs one. In the summer you reverse the scenario....oh well Im just learning and at least I dont have a "cold cycle" anymore!
Thanks everyone for your help! Dennis
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On Feb 10, 2:30 am, snipped-for-privacy@gmail.com wrote:

Have you looked in the furnace itself to determine whether there's a fan selection switch? Mine has one but a panel must be removed to get at it.
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After doing some digging around it would seem that some furnaces have two modes...Fan "On" and "Auto". Theres no mention of it in the furnace manual but Im starting to suspect my furnace has this option that can be set from the thermostat. The problem is my thermostat is one of those old kind with the mercury tube in it. No fan settings. Maybe the previous owner upgraded the furnace but not the thermostat. There's only two wires travelling from the furnace to the thermostat so even if I had a newer thermostat with a fan setting, there arent an fan wires to connect it too. Is it possible my furnace is stuck in "ON" mode?
Replace the thermostat. Get an electronic "set-back" t-stat, it not only has the on/auto switch, but can be programmed as well.
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Since he stated that he only has two wires going to his existing thermostat, just changing the thermostat isn't going to let him control the fan. He would also need to run additional wire connected to the furnace to allow fan control.
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For whatever reason, the fan is on continuous. This could be a low voltage wiring problem, or it could be a bad fan limit switch.
Call a repair company.
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Christopher A. Young
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