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Old 12-18-2011, 02:07 PM   #1
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no fan with "auto" setting on HEATING


Hoping someone can please assist me with fixing the wiring on my home's HVAC unit.

1970's home with original GE central heat unit w/ A/C condenser unit outside. When we purchased the home, inspection showed that HVAC unit had "hacked" wiring from someone in the past and it was not working properly. As part of the sale, some repair guy came out and got it all back and working just fine (so we thought). The serviceman came during the spring when neither heat nor cooling was needed and to show us it worked, we got a demo in the "ON" setting for force it on. When summer came along, the A/C worked like a charm and came on/off with the "AUTO" function as we had the thermostat set. When late fall came and it was time to switch to heat, we discovered that when using heat the fan will not turn on in the "auto" feature - but it does come on when set to "on". We don't use the heat that often, so everything's been fine and we just use the heater manually. Now I'm tired of this

SO...I opened up the cover panel on the heater and had a look at the wiring and found there are two wires that aren't connected to anything. I figure my issue has got to be with these being disconnected from their respective places. The first wire is a long, yellow wire what is cut and is coming from a cluster of 5 heavy-gauge wires originating from down below (where i'm assuming they're connected to the fan/blower motor) - I could not find the other cut piece of this yellow wire if it was indeed cut from something. The second wire is a short black wire that is capped with a wire nut and has visible signs of it originally being connected to something (due to the frayed nature of the wires partially exposed under the wire nut). This wire originates from the black controller that says "fan off" and has a temp setting on it w/lever arm. I'm assuming this controller has something to do with the heat in the heater unit itself and will control the fan if it gets too hot and prevents fire?

Here is a pic of the wiring followed by a pic of the serial plate. Any help would be greatly appreciated since money is tight and I have no idea how much an HVAC visit will cost.


little bit closer image w/o circles


serial plate

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Old 12-18-2011, 02:28 PM   #2
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no fan with "auto" setting on HEATING


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Originally Posted by perkolator View Post
Hoping someone can please assist me with fixing the wiring on my home's HVAC unit.

1970's home with original GE central heat unit w/ A/C condenser unit outside. When we purchased the home, inspection showed that HVAC unit had "hacked" wiring from someone in the past and it was not working properly. As part of the sale, some repair guy came out and got it all back and working just fine (so we thought). The serviceman came during the spring when neither heat nor cooling was needed and to show us it worked, we got a demo in the "ON" setting for force it on. When summer came along, the A/C worked like a charm and came on/off with the "AUTO" function as we had the thermostat set. When late fall came and it was time to switch to heat, we discovered that when using heat the fan will not turn on in the "auto" feature - but it does come on when set to "on". We don't use the heat that often, so everything's been fine and we just use the heater manually. Now I'm tired of this

SO...I opened up the cover panel on the heater and had a look at the wiring and found there are two wires that aren't connected to anything. I figure my issue has got to be with these being disconnected from their respective places. The first wire is a long, yellow wire what is cut and is coming from a cluster of 5 heavy-gauge wires originating from down below (where i'm assuming they're connected to the fan/blower motor) - I could not find the other cut piece of this yellow wire if it was indeed cut from something. The second wire is a short black wire that is capped with a wire nut and has visible signs of it originally being connected to something (due to the frayed nature of the wires partially exposed under the wire nut). This wire originates from the black controller that says "fan off" and has a temp setting on it w/lever arm. I'm assuming this controller has something to do with the heat in the heater unit itself and will control the fan if it gets too hot and prevents fire?

Here is a pic of the wiring followed by a pic of the serial plate. Any help would be greatly appreciated since money is tight and I have no idea how much an HVAC visit will cost.


little bit closer image w/o circles


serial plate

when i look at that picture the first thing that comes to my mind is "were the hell are the meatballs?" No plate of spaghetti should come with out meat balls.......

OK it look bad but its decipherable, the rectangular black thing in the middle of the 1 st and second picture is the fan/limit control.The red wire coming off that control carries the 120 vac signal down to the motor, the Black wire is the 120vac power to the fan/limit control, so first using a volt meter set to VAC see if you have power coming in, the of course see if it is going out to the motor......if there is 120 vac going to the motor and its not running, then you have a bad motor.

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Old 12-18-2011, 04:39 PM   #3
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no fan with "auto" setting on HEATING


Good grief, if the motor was bad it wouldn't come on in FAN on mode or in cooling.

That tear drop dial on the fan/limit switch, there's a slot you can use a flat head screwdriver to turn it with or you can simply use your fingers but be very careful as there is live electricity running through those wires through those spade terminals.

With the system on call for heat turn that dial all the way to the right, clockwise and see if the fan comes on then. If it does than goOd but I doubt it will. What you are doing is lowering the temperature it takes to activate the fan. You'll notice temperature numbers printed on that dial, 220 on the far left or since your unit is vertical, on top and 90 on the far right or bottom.

I changed one of those exact same fan limit switches only a few days ago on an old Rheem furnace. It cost $53 and change from the supply house.

Granted that's cost to an hvac company, probably cost you in the range of $300-$400 to have someone come out with it but it will be worth it.
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Old 12-18-2011, 04:47 PM   #4
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You've had serious issues with that furnace, those limits have been bypassed and rigged up. Might seriously consider a new furnace. Don't even consider it, just do it.

That yellow wire is to a high temperature limit switch or is supposed to be going to one. Apparently it's no longer in use which means the switch once tripped and is bad (non resettable) and someone removed it from circuit instead of installing a new one. It is a fire safety prevention switch that is not being used any longer so your furnace, home and family as well, are all unsafe. Might not be what you want to hear but it's the truth, plain and simple.

Black is a high voltage wire coming into the limit switch and back out to the fan or again, is supposed to be.

I do not believe that you will have heat under these conditions as there is no bypassing the fan limit, why you currently do not have heat.
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Old 12-18-2011, 07:33 PM   #5
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Here are some things to think about.
If you were to get a replacement from GE (now Trane) it would be a normal honeywell fan and limit ,probably with either an 8" or 5" incertion element.
The one thing that you can be sure of is that your furnace is 30% or more too big for your house (thats just what they did 25 years ago).This means that if you just sized the furnace correctly with another 70% furnace you could save 300-400 dollars in a heating season.Now think of what you could save with a high effient furnace sized correctly with a manuel "J".
This probably means your a/c is also grossly oversized costing you a lot more to cool your house in a cooling season.
There is no doubt that if you can find a compedent service guy he could fix and adjust your furnace reasonably, but why would you want to??? unless you are well off and heavy fuel costs don't bother you.
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Old 12-18-2011, 07:40 PM   #6
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call a furnace guy to check the wiring to your fan/limit switch.
before he spends a lot of time=your money have check the heat exchanger for cracks ,if he finds no cracks then have him fix the wiring
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Old 12-18-2011, 07:43 PM   #7
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All excellent points but they still make the exact same replacement, six wires total.

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Old 12-18-2011, 07:44 PM   #8
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everything i see in there is not safe..as mentioned already you don't bypass any needed controls ever ......GET A NEW FURNACE>>>>
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Old 12-18-2011, 09:21 PM   #9
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All excellent points but they still make the exact same replacement, six wires total.

Well I know that that Camstat F&L is still availiable but I don't think it is original to that furnace.If you look there is only 4 wires hooked up to it.
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Old 12-18-2011, 09:37 PM   #10
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The one I replaced the other day had a total of six. What you can not see in the pic are the two spades on the bottom.

On the one I replaced a few days ago those two wires, on bottom, connected in series to the temperature limit switch above the blower.
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Old 12-18-2011, 09:52 PM   #11
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You know me, pics of all jobs.

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Old 12-19-2011, 01:31 AM   #12
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Thank you all for your responses. It seems I have a real issue on my hands. I always knew it looked like a crackhead went at the wires, but thought it just "looked worse than actually is".

Quote:
Originally Posted by Doc Holliday View Post
You've had serious issues with that furnace, those limits have been bypassed and rigged up. Might seriously consider a new furnace. Don't even consider it, just do it.

That yellow wire is to a high temperature limit switch or is supposed to be going to one. Apparently it's no longer in use which means the switch once tripped and is bad (non resettable) and someone removed it from circuit instead of installing a new one. It is a fire safety prevention switch that is not being used any longer so your furnace, home and family as well, are all unsafe. Might not be what you want to hear but it's the truth, plain and simple.

Black is a high voltage wire coming into the limit switch and back out to the fan or again, is supposed to be.

I do not believe that you will have heat under these conditions as there is no bypassing the fan limit, why you currently do not have heat.
Doc - is this "limit switch" you refer to here different than the black box centered in unit? The one with the black, disconnected wire coming out? If its a different part can't I just add one in?

I mean the unit works fine on manual/ON mode, just not auto - so we do have gerryrigged heat. I can hear the thermostat click it's relay at the thermostat itself to give the on/off signal. The burners also will stop lighting once set temp has been achieved - so something is working. The burners also cycle on/off instead of straight burning nonstop. I'm assuming these intervals are being determined by a heat limit controller otherwise it would have just kept burning and most likely my house too.

I just want to get the fan to cycle on/off with the flame on auto mode. A new furnace or $300 visit from the hvac man isn't exactly in our budget right now, but a sensor/temp controller definitely is. If you think theres a part missing - i will get it. I can also take more, or clearer pics if needed - i should mention there are two transformers or relays behind the panel on the left that aren't in the pic. Dunno what those do, but they're there and are integrated with the wiring but seem intact. Once it's fixed I can zip tie the wires back and make a cover for them since the original is long gone.
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Old 12-19-2011, 04:48 AM   #13
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Thank you all for your responses. It seems I have a real issue on my hands. I always knew it looked like a crackhead went at the wires, but thought it just "looked worse than actually is".



Doc - is this "limit switch" you refer to here different than the black box centered in unit? The one with the black, disconnected wire coming out? If its a different part can't I just add one in?

I mean the unit works fine on manual/ON mode, just not auto - so we do have gerryrigged heat. I can hear the thermostat click it's relay at the thermostat itself to give the on/off signal. The burners also will stop lighting once set temp has been achieved - so something is working. The burners also cycle on/off instead of straight burning nonstop. I'm assuming these intervals are being determined by a heat limit controller otherwise it would have just kept burning and most likely my house too.

I just want to get the fan to cycle on/off with the flame on auto mode. A new furnace or $300 visit from the hvac man isn't exactly in our budget right now, but a sensor/temp controller definitely is. If you think theres a part missing - i will get it. I can also take more, or clearer pics if needed - i should mention there are two transformers or relays behind the panel on the left that aren't in the pic. Dunno what those do, but they're there and are integrated with the wiring but seem intact. Once it's fixed I can zip tie the wires back and make a cover for them since the original is long gone.
Some people on here tend to over dramatize things......yes your furnace"s wiring is in a state of disarray, and yes ANY furnace that is 20+ years old may have a crack or I'm-perfection in the heat exchanger and that is a serious issue if it exist in your furnace(chances are very low that it does) the part on your furnace that is bad is refereed to as a "cam stat" limit....a nd they are readily valuable at thousands of outlets all over the country.
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Old 12-19-2011, 09:57 AM   #14
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Ok, so I need a cam stat limit controller. Do you have a place to recommend purchasing one? I'm in Sacramento area but don't think I'll be able to get to a store during the week - so online retailer would be easier.

Are they all the same or is there a specific type I need to go with this old unit? Lastly, how do I wire said controller? Does it just have 2 connections (one for the yellow fan wire and one for the black wire off the heat sensor?) or is my wiring rigged beyond just 2 wires being in the wrong spot?

All this is seriously a big help. I can't believe the serviceman would leave the heater like this. But it was a few years ago now and we never noticed until like 9months after he left. You think the wiring looks bad now...shoulda seen it before he worked on it!

Cracks in heat exchanger - this would have to do with leaking burnt fuel/CO into the "clean" air right? I'm sure it can happen but I don't think ours has a crack.
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Old 12-19-2011, 10:28 AM   #15
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