Fan does not stop running on 40 year old furnace


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Old 01-26-14, 03:21 PM
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Fan does not stop running on 40 year old furnace

Hello,
I'm trying to help my dad with his heater. It has the name "Holly" on it and it is original to the house from the late '60s. It has been working fine and the heat goes on and off ok, but when heat stops, the fan just keeps running. It has an old thermostat so there is no "fan" switch on it, just the temp dial.
I've read some other postings here and it must by a stuck switch. He could give it a little hit and it would stop, but now that doesn't help anymore. It seems to have two switches and I'm wondering which one needs to be replaced.
I took some pictures:
holly furnace 1 | Flickr - Photo Sharing!
holly furnace 3 | Flickr - Photo Sharing!
holly furnace 4 | Flickr - Photo Sharing!
holly furnace 5 | Flickr - Photo Sharing!
holly furnace 6 | Flickr - Photo Sharing!
holly furnace 7 | Flickr - Photo Sharing!
 
  #2  
Old 01-26-14, 03:50 PM
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Welcome to the forums.

The following picture is your fan switch. The dead giveaway is where it says "fan on temp."

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Hard to find replacements for. The link below is one place.
That furnace is very old.....it should be inspected by a qualified HVAC technician for heat exchanger condition. A whole lot of money can be saved with a modern energy saving furnace. Doesn't have to be one of the top of the line models.

90F - 140F Adjustable Blower Temperature Switch Thermostat Snap Disc Fan | eBay

Looks different but should perform the same function.
 

Last edited by PJmax; 01-26-14 at 04:09 PM.
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Old 01-26-14, 04:21 PM
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Thank you very much for the reply. I was thinking that was it but could not find anything similar online. Thanks for the link too. I will try to talk my dad into getting the furnace checked out and maybe replaced. He is a bit hard to convince, we'll see!
He had the gas company come take a look at it, but that's it so far.
 
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Old 01-26-14, 04:23 PM
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I don't think that Thermo-Disc will work unless you can get one which extends about 3" into the cabinet. That switch looks very much like the old Cam-Stat fan controls.
Turn the power off to the furnace, remove the two screws holding the control in place, remove the control & measure the insertion depth.
You might be able to find something here: Camstat: HVAC Parts | eBay
 
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Old 01-26-14, 04:37 PM
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I could only find the similar in appearance switches in "open on rise" switching which won't work here. I can't tell how much of a probe is required here or what size it is.

The original part is a Therm-o-Disc AF-301.


Close/possible match
FAL7C05TD120A Fan switch - Amazon
 
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Old 01-26-14, 04:41 PM
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Searching on Grady's term "Thermo-Disc" + AF from your picture yielded a few hits. So you should try Therm-O-Disc + AF 3 + whatever it says under that wire.

Similar parts:

Carrier Parts - HH680100 - Fan Control - Therm-O-Disc AF156 F130F C8620
Carrier Parts HH680100 Fan Control Therm O Disc AF156 F130F C8620 | eBay

Carrier Bryant P331-1101 Fan Switch
Carrier Bryant P331 1101 Fan Switch | eBay

If you are handy you could use a volt meter to test the part and perhaps figure out why it is not working and if you can clean it or repair it.

If you really suspect that part has failed, you could remove it and bring in to your local reputable HVAC parts place. Even if they don't have the part they or one of the expert technicians their buying parts might be able to help you.
 
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Old 01-26-14, 04:48 PM
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The FAL7..... is a 7" insertion which might work but without knowing the insertion depth, we're all guessing.
 
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Old 01-26-14, 04:52 PM
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Honeywell has a fan/limit switch which you could use. It has different insertion lengths and you can manually set the air temp for what you want unlike today's switches.

If you go to pexsupply and type in Honeywell fan/limit they will come up and you can also see a wiring diagram for it.
It will take the place of both your fan and limit switches.
 
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Old 01-26-14, 06:17 PM
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thanks so much to everyone for all the info! I will be going over there on Tuesday to pull the part and I will check the switch out and measure the insertion depth.
 
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Old 01-26-14, 08:00 PM
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Use any 3" in fan switch,most were of the "fan off" style, only difference is you set the temp for the off temp not the on temp. That particular fan switch would give problems after a few years, try tapping on it and I bet the fan will go off.
 
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Old 01-27-14, 10:03 AM
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I spoke with my dad last night. He took the switch off and checked it out and tried to clean it a bit. He put it back and it seems to be working better for now, but I will try to purchase a replacement. He is in his late 80s and is good with electronics, but not with using computers and searching the internet I have also sent him all your suggestions so he can read them over.
I will try some of the links you have provided to find a compatible switch.
 
 

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