Gas Furnace blower comes back on several times after burners are off

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  #1  
Old 11-08-15, 02:24 PM
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Gas Furnace blower comes back on several times after burners are off

This condition of the blower coming back on about 3 separate times after the burner has turned off has been happening for seven years (since I've owned this) and is only annoying meaning the furnace does heat my townhome adequately. I've watched this happen meaning I've taken the cover off the face of the furnace and watched the burners go off, then after a minute or so the blower goes off as it's suppose to. Then after about a minutes (maybe 45 seconds) the blower goes back on without the burners firing on then turns back off within about 45 seconds, and then repeats once more or twice more. My limited knowledge is that the chamber temperature is high enough to signal the blower to come back on but then why did it go off too early to begin with? This Custom-Aire gas furnace was installed new back in about 1965. I live in Huntington Beach, CA so I hate to have to buy a new furnace (unless it's unsafe) because I only need it about 2.5 months/year, and there is no threat of pipes freezing, etc. Does anyone have any ideas on how to fix? Thanks. Name:  IMAG0357.jpg
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  #2  
Old 11-08-15, 03:27 PM
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Oh, I just remembered that in the summer, when it gets hotter than normal outside, that this will trigger the blower to turn on. It's like the chamber gets warm and triggers the blower to blow out until it's under a certain temperature. For the past few years (because this is annoying), I completely shut down the furnace (turn off the pilot and shut the gas off and unplug the electrical) to avoid this from happening.
 
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Old 11-09-15, 12:40 AM
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Welcome to the forums.

Your problem part on that 50 year old furnace is the fan control. It is the device with the "push up for heating" label. I don't recognize the manufacturer of that control.

Can you see any info on it ?

It looks to be externally adjustable and it's probably set too low which is why the blower comes on when it's hot in the summer.
 
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Old 11-09-15, 05:31 AM
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All switches used for on/off control, like your fan control, have hysteresis. In a furnace the hysteresis is the temperature difference between turn off and turn on. This is your problem. Your fan control switch needs a wider hysteresis.
The better switches have an adjustable hysteresis. Take your model number and search the web to see if there is an adjust. This is separate from the heat and cool slide control on the side of the fan control. If you find a manual for the fan control, check if it has an adjustable shield on the heat probe for controlling the control's sensitivity to the blowing air, You would have to remove the fan control to make any adjustment.
The furnace control circuit is an unusual design in that a call for heat by the thermostat does not turn on the fan motor. There is a high limit contact for protection should the fan motor not start.
Good luck.
 
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Old 11-09-15, 09:18 AM
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I've attached another angle of the fan control which shows the part number F124-11A-100-25C (Cam Stat). Google searching for the part number doesn't come up with any matches but I'm sure there is an equivalent available somewhere? I always have it adjusted to the upward most highest temperature which doesn't correct/help the situation. I guess if I could find an equivalent part to install I'd do that, any suggestion on how to find one?Name:  IMAG0356.jpg
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Old 11-09-15, 09:26 AM
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Thanks for everyone's reply, I really appreciate it. I would love to find a manual for the fan control but I can't even find a part number match.
 
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Old 11-09-15, 09:39 AM
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The furnace control circuit is an unusual design in that a call for heat by the thermostat does not turn on the fan motor.
Not at all.... this is an OLD furnace. An actual fan control was used to monitor plenum temperature for blower activation. They didn't even have a fan center where you could turn the blower on from the thermostat.

It looks like you're in luck as there is a replacement for your control. Your control is part number - F214-11A-100-25. The part in the links is a replacement for it......

F214-11A-110-25 Fan Control Camstat
F214-11A-110-25 Fan Control Camstat
 
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Old 11-09-15, 09:48 AM
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Oops, I goofed with F124, thanks for noticing that it's F214. It looks like the new ones in the links you sent have a setting that goes up to 120 degrees instead of the one I have that only goes to 100 degrees. This just might correct my situation. Do you think it's any safety issue where my actual furnace should have the high temp setting maximum of 100 degrees as the original equipment has? Thank you very much for noticing my number error and your advice.
 
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Old 11-09-15, 09:53 AM
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Just set it to 100 or 110.

It's supposed to be a repairman set device who would set it correctly for the furnace.
 
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Old 11-09-15, 12:35 PM
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Thanks, I'll use the 100 degree setting and maybe that will work and the old part is just malfunctioning, then adjust higher if 100 degrees doesn't fix the issue. Also, I notice the replacement part doesn't have the suffix "C" but there are other similar part numbers available that still have the "C" suffix and some that don't. Since my original part number has the "C", will having a part without the "C" be an issue do you think?
 
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Old 12-10-15, 08:23 AM
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Okay, so my replacement fan control has been on back order for a while now, and I just talked to the customer service rep where I order the part from and he now says there supplier says it's going to be another 30 days. The rep did say he has an equivalent part but it has a seven inch probe (the part this sticks back into the chamber of the furnace, sorry my terminology is probably not accurate) and if that will fit it should work the same as the originial part with a 3 inch probe. Can anyone say if the seven inch part will work the same? Thanks,
 
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Old 12-10-15, 09:11 AM
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It will work ok but without measuring there's no way of knowing if the plenum is deep enough at that point to allow installation. That's probably a part that once you buy it.... it's yours.
 
  #13  
Old 12-10-15, 11:37 AM
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This is an "off" temp setting switch. If you set at 100 it comes on at 125. 100 is too high an off temp. Try setting it at 80 and see how that feels or maybe 90. Very popular brand years ago.
 
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Old 12-10-15, 12:09 PM
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Thanks mbk3. So trying to get my brain wrapped around what you said and the function of this fan switch, in other words, when the furnace burners are fired on, then they go off, the fan still runs to cool down the chamber, so if I want the fan to run longer to cool down ever more, set the temperature lower like you said.

I think I've got it. I'll try reinstalling tonight and let everyone know the outcome. Thanks.
 
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Old 12-10-15, 07:49 PM
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Regardless of where the old one is set.... it will still cycle on and off several times.
 
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Old 12-12-15, 02:26 PM
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Okay, so I finally had time to reinstall the old fan switch and set it to 80 degrees F. Got everything connected back together, then turned on the pilot light, then turned on the thermostat, set temperature 1 degree above ambient, then furnace burners fired up as they should, then about a minute later the fan turned on as it should. Furnace burners turned off and fan kept running... and running... and running when after about 12 minutes the fan never shut off so I turned up the fan setting and it immediately turned the fan off after barely inching the fan switch temp setting higher.

So I set the fan switch to 90 degrees. Let everything alone for about 20 minutes, then turn thermostat to one degree above ambient to fire up the burners. After the burners turned off, the fan shut off about 4-5 minutes after. The fan went back on after another 4-5 minutes without the burners firing up then stopped after about one minute. Then the fan came back on again after 5-6 minutes without the burners firing up then stopped after being on less than a minute (prob. 30-45 seconds). Then after 9-10 minutes the fan turned back on again without the burners firing up and turned off in about 30 seconds. Then after about 15-16 minutes, the fan came on again, then turned off in about 20 seconds.

So that's four times the fan came on without the burners turning on so trying different fan switch temp settings didn't help though I think it changed the time between the fan turning on and off to a longer time.

Looks like I'm back to ground zero but the wife's happy that we have heat (note we live in Southern California so I'm not making her freeze, when it get's in the high 40's at night, in the house it only gets down to about 62 or 63 but that's after we go to bed).

I did look inside and it should accept the 7" fan switch so I guess I'll order that one. Thanks everyone for your help.
 
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Old 12-12-15, 02:35 PM
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So the fan just went on briefly for a fifth time!

Just wondering, I've always thought that my pilot light is larger than normal compared to what I remember. Attached are pictures of the pilot light and it's only 16" directly below the fan switch, do you think that the pilot light is heating things up (or not letting it cool down) and this contributes or causes my problem?Name:  IMAG0482.jpg
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  #18  
Old 12-12-15, 03:35 PM
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It does appear from your pics the pilot is too large and needs cleaning.
 
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Old 12-12-15, 04:11 PM
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It also appears the control may be fatigued after all these years. Be sure to verify all of the registers are open too.
 
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Old 12-12-15, 04:58 PM
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@mbk3: What part is the control?

Also, another piece to the puzzle: I had been out in the garage since working on the furnace today. When I came back in the fan was running. Note that the thermostat control had been turned off. So, I took a shower and it was running again when I got out of the shower so it appears it had been turning on about every 10 minutes or so. About 20 minutes ago, I turned the fan control temp setting to the highest at 100 degrees and so far the fan hasn't come on.
 
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Old 12-12-15, 05:22 PM
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I don't see where any of us mentioned to check the filters. Control is the fan switch. Just another term.
 

Last edited by mbk3; 12-12-15 at 05:25 PM. Reason: More info
  #22  
Old 12-12-15, 05:56 PM
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I installed a new filter. Note that the filter had to be hand cut because it's behind an are where you have to turn it on it's side then bend around until it's flat in covering the air intake area. Plus the size isn't available in a standard store off the shelf product.
 
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Old 12-14-15, 01:06 PM
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I probably won't be trying to install a new fan switch until January. How does one clean the pilot? Yeah, I think the pilot is too high. I used to not turn off the pilot in the summer months but now I do. Turning the pilot off saves me $10 to $12 a month, that probably is an indicator that the pilot is too high.
 
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Old 12-14-15, 04:12 PM
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Maybe you could call the Gas co and they will clean and adjust for you?
 
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Old 12-14-15, 08:33 PM
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that furnace needs to be canned; otherwise completely serviced.

based on the look of that pilot it may not even have an orifice, have the wrong orifice or the pilot pressure is wrong.
 
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