Fraser Johnston furnace model #125 C 21 problems

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Old 12-09-19, 04:30 PM
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Question Fraser Johnston furnace model #125 C 21 problems

At first the furnace was short cycling... running for a minute then shutting down completely. Cleaned it some with a vacuum & removed some “dust bunnies”, tried lightning it again & it ran for roughly six hours before completely shutting down again. Removed replaced the thermocouple with a new Honeywell CQ100A1013 thermocouple. The pilot light ignites, but the furnace burners aren’t lighting. I don’t smell any gas. The power is on to the furnace when I turned up the thermostat dial, but no activity from the furnace. Currently the power is off, but the pilot light is lit.

Looking for suggestions on what (& how) to check next to try & get the furnace going again.
Don’t want to deal with a service that is more interested in trying to sell us a new furnace than get the old one working again.

The pilot light & thermocouple inserts into the burner chamber connected to a rail that screw mounts onto the rightmost burner tube. The pilot light is heating up the new thermocouple.

The old thermocouple for reference & verify I got correct replacement thermocouple.

See pictures and link in my next post.
 

Last edited by PJmax; 12-12-19 at 06:54 PM. Reason: removed links per member
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Old 12-09-19, 09:16 PM
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Welcome to the forums.

That's a pretty old furnace. I hope you've had it professionally cleaned and inspected. Furnaces don't last forever. Heat exchangers rust and rot thru with age allowing CO to enter the house air stream.

The thermocouples only job is to keep the pilot lit.

That's a 24v gas valve so there is something keeping it from getting 24v. It could be a defective or tripped limit switch. I'd need a photo of the wiring diagram that should be posted on the back of the blower door.
 
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Old 12-11-19, 07:45 PM
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I checked the back of the blower panel, but either the diagram was so old the glue dried & it was thrown away ... or there wasn’t a diagram on the panel.

I’ve taken more photos & switched the photos over to Imgur. Found out google photo links give too much access to your account & need to delete the links, but the edit button isn’t available on the post.
https://imgur.com/gallery/dmnNVd5

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Last edited by PJmax; 12-12-19 at 06:58 PM. Reason: imported 1 important picture
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Old 12-11-19, 09:27 PM
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I’m seeing rust and signs of rollout on that furnace. When was the last time it was cleaned and tuned up?
Old equipment is fine. As long as it’s safe.
 
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Old 12-12-19, 07:03 PM
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I removed your links form your post. Most of your pictures aren't really needed. As mentioned.... one shows a lot of rust which is an indication of internal rusting.

I imported one picture.
You'll see three connections and four wires. The cable is 24v from your thermostat. The two red wires look like some type of safety. On a call for heat..... you should measure 24vAC on your two thermostat wires. If the switch from those two red wires was ok..... you'd measure 24v across the two outside terminals and the valve would be open. I have a feeling those two red wires are open...... and should be closed (shorted).
 
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Old 12-13-19, 01:13 AM
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Good news, the furnace started back up. There was a circuit breaker (I think) on the furnace itself. But now the blower starts up as soon as the electricity is turned on & won’t turn off.
The guy we got to look at the furnace may have changed the setting of a dial &/or the temperature cut off. But I don’t know if that is related to the blower not switching off.
Anyone here know what settings these should be at?

Note the “circuit breaker” is on the left of the box. Pretty sure the slide dial on the right is the emergency temperature cut off. The round dial appears to have the settings Lo, A, B, C, & D. Have no clue what that does or should be set at.

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Last edited by PJmax; 12-13-19 at 05:08 PM. Reason: imported/resized/labeled pictures
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Old 12-13-19, 03:37 PM
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Thank you PJMax. Appreciate you removing the google photo links!
 
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Old 12-13-19, 05:14 PM
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Pictures are good. They give me the ability to help you.

Look at the top picture. That is nothing more than an ON or OFF switch. When it's on..... the blower runs non stop. When it's turned off...... the blower is thermally controlled. Turn it off.

In the second picture. That's the thermostatic blower control. The red arrow is pointing to the turn off temperature which looks like it's set for 95°. Your blower will turn off when the furnace cools off to 95°. That's fine. The differential is the temperature when the blower turns on. It's a certain percentage over the off temperature. You want the blower to come on 20°-25° above the turn off temperature. I'd leave it where it was set.
 
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Old 12-15-19, 08:42 PM
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Blower won't shut off - Fraser Johnston furnace model #125 C 521

Got the furnace started up again, but the controls got changed, and now the only way to get the blower to shut off is to turn off the power at the main switch on the ceiling.
I got the blower to shut off once by turning up the temperature on the blower control, but couldn't get it to work a 2nd time. Plus I didn't want to keep changing the control on a 43+ year old furnace.
I was told the switch on the left side switches the blower between (forward) automatic- i.e. controlledby the furnace & (back) on. It was working, but now doesn't change from being on all the time.

Any suggestions on how to fix this?
Some pictures of the controls in a covered panel.
https://imgur.com/gallery/695e95S
 

Last edited by Trollz812; 12-15-19 at 09:38 PM.
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Old 12-15-19, 10:09 PM
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Threads combined. I answered this yesterday.
If that blower control goes bad..... you'll be out of luck.
I have not seen a replacement for that type of control.
 
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Old 12-16-19, 01:02 AM
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Sorry about posting a new thread.
Just thought that controller got set wrong, and if I could set it correctly ... the blower would work correctly again.
Do you know what the dial does? It has letters that completely confuses me.
Is there a chance to replace the switch? (Still don’t know which is the on position & which is controller operated...) Or does it sound like it isn’t the problem?
If we’re stuck with the blower stuck on, do you think we could Jerry-rig a timer to turn on the power for 2-2.5 hours in the morning?

Replacing the furnace right now isn’t possible. Just trying to either fix the old one, or figure out a way to get a working work-a-round that can get us through the next three months.
 
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Old 12-16-19, 12:55 PM
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You can disconnect that toggle switch from the heat thermostat. It's only for manual blower override.
I explained the settings. The disc is called differential. You set the slide for TURN OFF temperature. The differential controls when the blower turns on.

Yours is currently set to turn off at 95f.
ON at.....
Lo = 100f
A = 110f
B = 120f
C = 130f
D = 140f
These values are just a guess but should be close.
 
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Old 12-16-19, 04:56 PM
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Thank you very much for the information! At least now I have an idea of what to talk about with the furnace people.
I really appreciate your time & assistance!
 
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