# Fan / limiter switch replacement



## REP (Jul 24, 2011)

That is what GE (Trane) would have given you 30 years ago when they stopped making that unique F&L control.
The Honeywell will be the opposite I.E. the black wire will go on the bottom.I'm not sure about the red and yellow wire.I think the red is fan and the yellow is limit but I am not certain its been a long time.Just follow the wiring diagram on the furnace pannel and it will show you what is what.


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## ben's plumbing (Oct 6, 2011)

Cysnake said:


> What a wealth of knowlege on this site! :thumbsup: I was hoping someone could give me a little advice. I have an old GE oil furnace model 21 that I have been pampering every year until i can afford to replace the system.
> 
> 
> 
> ...


 yes it should work... wiring changes I think not sure just look at diagram with unit it will tell you..:yes::yes:


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## how (Feb 26, 2011)

Your black wire on your old control is the power supply for new honeywell fan/limit control. The color coding for your fan & limit controls suprises me. If you are sure which is which then the honey well control is marked with fan & limit for the two connections furthest from where the lines enter the control.. Leave the breakable jumper in place. 
If you are not absolutely sure which is the fan line and which is the limit line .......Follow your red & yellow line from your old fan/limit control to the next junction box that the jacketed cable goes to. The limit will go to the burner or to power the transformer while the fan line will go to the blower.


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## Cysnake (Apr 17, 2012)

Thanks everyone! I wouldve thought the reverse for the black wire. I was 99% sure that wouldve been the ground because it was connected to both. Ive torn this furnace apart and rebuilt it so many times, but this is the first time ive hhad to deal witth the switch. Hopefully i can be of some assistance to you all in the future! The red wire should be the fan, atleast thats what it says on the microswitch its.connected to and same for the yellow. Thanks Again!
Chris


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## how (Feb 26, 2011)

Yeah, it's connected to both as a common power source for both switches. The new honeywell control uses the same set up except it uses a small built in brass jumper to connect both controls.


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## Cysnake (Apr 17, 2012)

Ok, one more small snag. Just measured and i have a 3" insertion limit. Can anyone recommend a different switch? The one i was looking at is a 5" insertion.


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## how (Feb 26, 2011)

Is it a 5" vent pipe? If so, perhaps a couple of washers around the probe will allow the honeywell control to work.


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## REP (Jul 24, 2011)

If you indeed hit the heat exchanger with that 5" incertion at the spot the old F&L was located,you will have to relocate it in the plenum as close to the heat exchanger as possible.It won't look pretty but it will work and it is what GE told people to do in exactly your situation.


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## Cysnake (Apr 17, 2012)

In my first pic of the furnace i just realized that coming off the pipe in the front is another fan limiter switch that is not connected, is this an acceptable place to mount a new switch, or could i drill through the plate in the back of the old switch hole to accomodate for a 5" insertion instead of a 3"?


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## REP (Jul 24, 2011)

That relay is not a fan limiter switch,it is a pyrostat which is a safty switch for the burner.
If when you try to incert the 5" probe ,you hit the heat exchanger,you cannot use the F&L in that spot.
If you were to try to drill in that spot you would damage the heat exchanger.
See my above reply to see where to put that honeywell F&L if you can't put it where the old one was.


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## beenthere (Oct 11, 2008)

Check into a camstat fan limit switch. they have 3" inserts.


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## Cysnake (Apr 17, 2012)

Ill check into the camstats. Thanks Again!


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## hvac5646 (May 1, 2011)

beenthere said:


> Check into a camstat fan limit switch. they have 3" inserts.


Not rated to be in oil flue path.


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## beenthere (Oct 11, 2008)

hvac5646 said:


> Not rated to be in oil flue path.


he's talking about the old fan limit, not the old stack control he also has. Which looks to have already been disconnected when the put a new burner in.


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## hvac5646 (May 1, 2011)

that's what i said.


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## Cysnake (Apr 17, 2012)

Ok, i got a camstat fal3c-05td-120-a. I cant seem to find any instructions on connecting it and setting it. Can someone please walk me through? I have read to set it according to the old one. Well i cant do that because the old one disintegrated. They are also not clear on where to connect the wires. I have 3 wires, a power wire, fan and a limiter wire, i cant figure out what terminals they go on. Thanks everybody for all your.help so far!


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## how (Feb 26, 2011)

How many terminals are on your cam stat control?
Cam stat controls usually come with a schematic that assigns numbers to the wires that correspond to the numbers beside the control terminals.


A continuity test between the Cam stat power terminal and the Cam stat blower terminal will show the control to be open. The same test between the Cam stat power terminal and the cam stat limit terminal will be closed.


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## Cysnake (Apr 17, 2012)

I found the schematic, this is what im thinking. There are 4 terminals on the camstat, numbers 2. 4. 5. And 6. Im thinking the power wire needs to go to terminals 2 & 6, and the fan wire goes to terminal 4 and limiter to terminal 5. But looking at the schematic it is calling for a 24 volt transformer for #6 terminal for the limiter. My old switch didnt have a transformer, both the fan and limiter were wired together at 120. Do i need a transformer?


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## Cysnake (Apr 17, 2012)

Stealing an image from another member on here (thanks! If its a no no, i will remove it) but here is the schematic


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## beenthere (Oct 11, 2008)

Yes, 2 and 6 would be jumpered together, then 4 is the fan and 5 is the limit.


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## how (Feb 26, 2011)

In this case the schematic does not match your system (accordiing to the photos you posted of your old fan/limit).
You do not need to worry about any 24V in this wiring set up. The safety limit system on your system powers the furnace transformer with 120V instead tapping into the 24V side of the safety circuit like the schematic shows.


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## Cysnake (Apr 17, 2012)

Thanks so much again! What would you reccommend setting the temp.adjust to? And should i adjust the limiter or leave it as is?


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## Cysnake (Apr 17, 2012)

Ok, switch is in, however i cant get it to turn the blower on. I let the furnace.run for 5 minutes and it wont start. Blower runs if its in the "on" position on the thermostat. What have i missed? Do i need to adjust something on the camstat?


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## Cysnake (Apr 17, 2012)

Ok, figured it out, my dumb mistake. All i need to know is what i should set the fan differential to. I set the fan off at 90


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## beenthere (Oct 11, 2008)

You want it to come on at around 120 to 130.


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## Cysnake (Apr 17, 2012)

I have a heat pump on this furnace as well, the thermostat seems to control the camstat. I dont think the camstat is turning on the fan by temp. I had the thermostat turned off and jumped the furnace terminals to light it. I let it run for 5 minutes and the blower didnt.come on. Once i turned on the thermosstat and cranked the temp up the blower kicked on with the heat pump. The furnace itself has not run yet. The fan differential knob is really throwing me for a loop, i cant find anything on the net that tells me what it does, or how to set it. It has off, low, A, B, C, and hi. The old switch was really straight forward in how it operated. Sorry im such a novice when it comes to this section of the furnace, and i appreciate all your patience with me!


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## beenthere (Oct 11, 2008)

On that camstat, you set the off temp, and then set the diff for your on temp. So if off is 90, a diff of 25 will bring the fan on at 115.

Jumper across terminals 2 and 4. The blower should come on.


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## Cysnake (Apr 17, 2012)

Ok, my off temp is 90 and i set the diff to "B" cause its in the middle. Eveything seems to work except when the furnace.turns off, so does.the blower. The blower should run for a few.minutes after the furnace shuts off. I just set the diff to B so im checking to.see if that has an effect


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## beenthere (Oct 11, 2008)

Do you have the black wire on 2 and 6, the fan of 4, and the burner on 5.


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## Cysnake (Apr 17, 2012)

Yep, thats the way i wired it. Even with the thermostat off, i was able to jump #2 and #4 together and the fan would run, Just cant seem to get it to start on its own via furnace temp. I did have to mount the camstat sideways into the pre existing hole for the old one, but that shouldnt have an effect on it, would it? heres a pic, the brown is connected to the black power wire. Sorry so blurry, couldnt get a good pic this morning and was rushed before work. Red is fan and yellow is furnace.


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## hvac5646 (May 1, 2011)

heat assisted cam-stat....takes 24 volts from a gas valve.


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## beenthere (Oct 11, 2008)

Just curious. When the old fan limit worked. How long did the furnace run before the fan came on? I have my oil furnae down fired really low, so it takes almost 10 minutes fr it to come on when I first come home and its been off all day(my basement gets really cold then). On average i would say it takes 7 to 10 minutes before my fan comes on. 

Run your furnace again, and check how hot the supply plenum is or isn't after 5 minutes, then 7 minutes then 10. If it is real hot, the cam stat may be defective, if not real hot, then its just going to take it how ever long to start the fan.


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## hvac5646 (May 1, 2011)

Don't do oil but based on what has been posted, the heat assist feature of Com Stat should be used.


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## how (Feb 26, 2011)

Hey HVAC6546
Any cam stat fan/limit control with heat assist that I've seen requires 6 terminals to work? I only see 4 on the pic?

I'd also like to see a clearer picture that shows the designation marks of the terminals just to ensure it's been connected up properly. 
Can you turn the temp adjustment down low enough to get the blower to engage with a 8 min heat run?? Try setting the "diff" to low or "A" to help.


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## hvac5646 (May 1, 2011)

how said:


> Hey HVAC6546
> Any cam stat fan/limit control with heat assist that I've seen requires 6 terminals to work? I only see 4 on the pic?
> 
> I'd also like to see a clearer picture that shows the designation marks of the terminals just to ensure it's been connected up properly.
> Can you turn the temp adjustment down low enough to get the blower to engage with a 8 min heat run?? Try setting the "diff" to low or "A" to help.


I could not tell from the pic either...was just saying he should use the Cam Stat with heat assist.


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## hvac5646 (May 1, 2011)

this is fan only.


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## how (Feb 26, 2011)

Hey HVAC5646
Not sure what you mean with the photo.

The Cam-stat Fal3c 05td-120 that the op listed is a combination fan & limit control although I do have 5" versions of it in my truck with an additional preheater. Usually reserved for counter flows that need an earlier blower start than conventional fan/limits can provide.


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## Cysnake (Apr 17, 2012)

Ill give it a shot tonight, ill se it to low and let the furnace run, i think its not getting hot enought where the switch is to kick it on. The old switch has those half loop bars on the end that you can see in the pics, im thinking they were up high enough to go over the metal guard by the heat exchanger, the camstat goes straight in and does not go above it.


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## ron2014 (Feb 16, 2014)

need help with a camstat 3 '' fan limit switch


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