# Old furnace fan blowintg 24/7. Wiring question.



## grantb5 (Sep 9, 2011)

I have a Gaffers and Sattler U80-1 gas furnace circa 1974 that blows all the time. I think the termostat portion is OK. The only way I can get it to stop is to unplug it (the furnace) from 110vac. :wink:

I looked at the wiring and the transformer is outputting 28VAC and it's got 24v written on it so I assume that's OK. I checked the thermostat with a meter and the relay is working OK. It's a 2-wire thermostat, powered by AA batteries (which are now brand new). So I think something on the other side of the transformer is closed when it should be open. 

I'm just guessing here but I think the thermostat controls only the flame and some other sensor turns the blower on/off (see diagram).










There is a big two-wire switch of some kind or other that is closed. It has a screw adjustment for voltage (I assume) marked 80-90-100 ... 120-FAN OFF. What is this? There are also two wires going into the guts that I have not had a chance to measure, but imagine they might be the culprit? Any recommendations? The gas is still on (pilot only), so should I kill that before proceeding? I have a DMM. Thanks!!


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## Dr.HVAC (Sep 8, 2011)

Does the stat have rc and rh terminals?


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## JJboy (Oct 12, 2010)

Check your thermostat :thumbsup:


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## grantb5 (Sep 9, 2011)

Switch in question..


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## JJboy (Oct 12, 2010)

can you post a picture with an overview


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## grantb5 (Sep 9, 2011)

I think the thermostat is OK. It doesn't control the fan anyway and the flame is not going other than pilot (I think) ... though maybe I should double check that ;-)


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## JJboy (Oct 12, 2010)

Sounds like the fan switch is close all the time.


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## Dr.HVAC (Sep 8, 2011)

Agreed. Something that vintage wouldn't have a battery stat, the g circuit (or even full on) can happen by not splitting r circuits. I've also seen g tied into an r at the unit to allow not running a 3 wire to the stat, which produces that same result.


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## grantb5 (Sep 9, 2011)

Is the fan switch the blue thing? Where do I get a replacement? What are the other two wires that disappear into the guts (you can see them in the 2nd photo in front of the blue thing).

Another question, the blower motor is quite noisy. Are replacements easy to come by?


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## Dr.HVAC (Sep 8, 2011)

That looks like some odd style of fan/limit I think?


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## Dr.HVAC (Sep 8, 2011)

It still should be verified first that there is a separation of heat to fan modes. With two wires to the stat the fan only will come on for a call for heat. Make sure that only wires are where they should be and nothing is bypassed.

Next, you will need to reset your limit fan thing there to open only when the appropriate temp is reached (I'm pretty sure that's what "the blue thing" is)

Lastly, check the capacitor and confirm the motor doesn't need to be lubricated


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## JJboy (Oct 12, 2010)

grantb5 said:


> Is the fan switch the blue thing? Where do I get a replacement? What are the other two wires that disappear into the guts (you can see them in the 2nd photo in front of the blue thing).
> 
> Another question, the blower motor is quite noisy. Are replacements easy to come by?



You have only 2 wires on Fan SW....one goes to motor and the another wire to L1.


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## grantb5 (Sep 9, 2011)

Maybe this part?

http://www.americanhvacparts.com/Me...=PROD&Category_Code=FL&Product_Code=FAN680201


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## JJboy (Oct 12, 2010)

grantb5 said:


> Maybe this part?
> 
> http://www.americanhvacparts.com/Me...=PROD&Category_Code=FL&Product_Code=FAN680201



Yes, To be sure disconnect the two wires and do a test ..... if it shows 0 ohms between the 2 wires you have to replace it.:thumbsup:


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## REP (Jul 24, 2011)

Nice find Grant,The part number is right there 40T3.
Just make sure you install it with the instructions because that line also feeds the transformer.


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## grantb5 (Sep 9, 2011)

I found it here and these guys seem to have a better reputation. 

http://www.partsguy.com/cgi-bin/PartsGuy/L36847.html

If there is a problem with physical fit, is it acceptable practice to construct a metal adapter plate or similar?


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## grantb5 (Sep 9, 2011)

OK I installed it and it seems to work. The new one had 4 wire terminals, two (optional) of which had something to do with the thermostat. In my case I just went with the original wiring where the fan runs on heat it senses only. BTW the box calls it a CAM STAT whatever that means. There is a better photo of it here out on the web:










And here too: http://www.furnacepartsoutlet.com/p...3TD-120-25C_fan_limit_control__93417_zoom.jpg

So regarding adjustment... I think the fan runs a little longer than it should at the end of the heating cycle. It tends to blow a little cool-ish air before it finally shuts off. The temp is set for 95 out of a range of about 90 to 120. That's how the old one was set(95). So should I raise the dial a bit to say 100?

---

_Educational link for self, included for posterity: http://toad.net/~jsmeenen/blower.html_


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