Furnace blows cool air when target temp reached

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Old 12-06-07, 07:13 PM
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Furnace blows cool air when target temp reached

All,

I am new to the forum and also just purchased a TH with a very old GE air forced gas furnace (installed 30 years or so ago). My issue is that it appears that the furance blows cool air when the target temp is reached according to the programmable thermostat. For example, at 5pm the furnace is set to to go to 72 degrees. Once the internal temp reaches 72 degrees the furnace appears to continue blowing cool air instead of shutting off. I don't know anything about furnaces, but I don't recall any working like this one. Is this normal or is something going wrong?
 
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Old 12-06-07, 07:30 PM
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Is the fan switch at the t-stat switch to ON from AUTO?

If it's on, the the blower won't shut off.. But if it's set to AUTO, and the fan never shuts off or does it shut after about X amount of min?
 
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Old 12-06-07, 07:49 PM
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Originally Posted by Jay11J View Post
Is the fan switch at the t-stat switch to ON from AUTO?

If it's on, the the blower won't shut off.. But if it's set to AUTO, and the fan never shuts off or does it shut after about X amount of min?

Its set to Auto. It seems like the fan does not shut off. Like now the temp is set to 71 and the thermostat says its 72 in the house. I'd expect the furnace to be off until temp drops below 71, but I can feel cool air coming out of the vents.
 
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Old 12-06-07, 07:59 PM
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71˚ is kinda warm....

Your old furnace will have a fan limit control, the fan limit control may not be moving to shut down the blower.

Is' in a silver box, behind that cover, is a dial, and 3 tabs, let us know what the tabs are set at for temp.

 
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Old 12-08-07, 09:27 AM
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I looked for that but did not see it. I did find the unit is a GE Gas Fired Warm Air Furnace. I also pulled off a cover and saw the filter, which is nice and clean and was able to see the pilot light going. I am going to snap a picture of what I see and upload. There is a swith in there that says fan and ignite, and I can see where it appears to be a blue hatch mark drawn on it. I also see that the humidity switch is at O when there are options of -10, -20 or +10, +20.

Also says direct blower at temps 70 - 100, static pressure point .50. Does that mean it will blow like that as long as the temp is between that range? If I set the t-stat to 69 will the fan stop blowing?
 

Last edited by azucarnegra; 12-08-07 at 09:36 AM. Reason: Add'l info added
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Old 12-08-07, 09:47 AM
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I am not sure what you got there???

I'll be waiting for the photo. if you can't upload it , e mail it to me.
 
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Old 12-08-07, 09:54 AM
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Not sure how to upload here. What's the email I can send too.

I sent to the one in your profile. My message may go to spam. Its coming from an AOL account
 
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Old 12-08-07, 02:46 PM
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Got it... Thanks..




I've never seen this type of set up..... Let alone with humidity, and static???

Is there a brand/make, and model # on this?

If I am guessing right, your fan comes on when the heat exchanger is 100˚, and off at 70˚. You keep your heat at 72˚, the fan will never shut off... Move it up to 80˚ and 120˚
 
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Old 12-09-07, 12:51 PM
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Here is what is on the unit:

Model: 21LU 080A 2M1
SN: 769267
Volts: 115
Direct blower: 70 - 100

I don't think I am able to change the fan info to 80-120. That is unless you can walk me through it. I am unsure if its better to switch back to 69 degrees with no blower or stay at 71. I may test it out to see if it feel warmer. I got some room thermometers to test the temp in the bedroom, which appears to be the coldest place in teh house and its around 68 degrees.
 
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Old 12-09-07, 01:22 PM
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I wish the photo of that fan switch was more clear. Are the 3 holes (one on left that says fan and two on right), to allow someone to put a screwdriver in them to turn recessed screws?

(Maybe it doesn't say FAN - it almost looks like KAN)
 
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Old 12-09-07, 01:43 PM
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Sorry, I took it with my camera phone. Can't find a flash light amongst the packed stuff.

The photographed unit says FAN on one side and LIMIT on the other. It has two holes that maybe a screwdriver can be inserted in under each side (fan, limit). It look like something may have broken off, but there is a little hatch mark drawn on the dial that is there. It look like I could turn it but I am afraid I might mess something up.

I guess I'll just have to say it'll stay like that unless I set the temp back to 69. Otherwise I'll have to have a technician come up and look at it.
 
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Old 12-09-07, 02:12 PM
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Okay. And because we all seem to be guessing here I can guess again and say maybe the holes are for wire connections access, or for being able to release the wires from a spring connector (where the wires are forced in from the bottom; then to get them back out you poke screwdriver in those holes to release them) - and this fan switch is preset with a thermodisc on back side for the fan.

Let us know what ends up coming of this situation, please.
 
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Old 12-09-07, 06:05 PM
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Of the info you've given me, I am not able to pull anything up.. GE has not made furnace since the early 80's....

So yes, call for service. and see what they come up with.. .

have you thought about a new furnace?
 
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Old 12-10-07, 04:59 PM
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We will look into new furnace in a few years. As the old saying goes 'if it ain't broke, don't fix it'. We just moved in so I'll have to see how the electric bill looks.

I changed the t-stat to have heat kick on at 69 degrees and the fan kept right on blowing. I gave it some time to maybe get the message and cut off, but it did not. I don't know, but for now I'll leave it alone.

The inspector said the unit is the original one from when the home was built. A technician who did some work on the furance said the same and that GE does not make furnaces anymore.

any recommendations one to get to heat a 3 level TH.
 
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Old 12-10-07, 05:40 PM
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Have you tried to see if you can order or buy another one of these fan/limit switches? Most likely, if you see no settings to adjust, is that it is preset thermodisc type on both the fan and limit portions and it has gone weak and you need a new one. That is my guess. I used to have to replace these discs all the time in old gas mobile home furnaces in the old days.

Thought of something else: There isn't something to turn or pull out/push in on that switch is there?, that might allow the fan to run all the time? But this would not be true unless the blower literally ran ALL the time. But yours is off before the furnace fires up the first time, and only runs on indefinitely after wards?
 
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Old 12-12-07, 05:30 PM
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From my research the blower is always running.

I haven't pushed, pulled or tweeked anything for fear of breaking it.
 
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Old 12-12-07, 05:50 PM
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As the old saying goes 'if it ain't broke, don't fix it'. We just moved in so I'll have to see how the electric bill looks.
It may not be broke but a 30+ year old furnace sends approximately half of its heat right up the chimney. If it hasn't been maintained, it's less than 50% efficient.

The heat exchanger; the part that separates the combustion gasses (exhaust) from the air stream, is most likely cracked. A large enough crack in conjunction with poor combustion (dirty burners, over/underfired, insufficient oxygen for combustion) can result in carbon monoxide poisoning.

Replacing it now will cost less than waiting for something to go wrong in the long run (savings on gas bill); usually when something fails, it does so at the least convenient time.
 
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Old 12-14-07, 04:53 PM
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Some repairs took place before we purchased. I'll pull to see what was done and come back then. I am also awaiting my first gas bill, since I have a programmable t-stat I am expecting it to be reasonable.
 
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