Low voltage short in furnace


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Old 12-21-19, 05:49 AM
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Low voltage short in furnace

I have a low voltage short when calling for heat. I know it's some where in roll out switch circuit cause when I unplug one it does trip fuse.

Can someone tell me what I should test down stream.

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Last edited by PJmax; 12-21-19 at 10:09 AM. Reason: reoriented/resized/enhanced picture
  #2  
Old 12-21-19, 10:12 AM
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Welcome to the forums.

Unplugging anything should not make the circuit breaker trip.

I added red and white arrows to your diagram.
The red arrows are pointing the always live 24vAC to the thermostat.
The white arrows are pointing the switched 24vAC line during a call for heat.

If the breaker trips on a call for heat.... the problem is in the white arrow line.
The rollout switches are in the red arrow line.
 
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Old 12-22-19, 06:08 AM
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What I mean is the circuit breaker trips is the roll out is plugged in. if I unplug the rollout the unit no longer trips. that's the only thing that I unplug that stops circuit breaker from tripping. Is that related to that circuit you highlighted in red ?
 
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Old 12-22-19, 08:15 AM
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The circuit starts at the red arrow by the transformer. You can follow the arrows all the way thru the circuit.

As previously mentioned..... if the problem only happens during a call for heat..... the problem area or device is in the white arrow line. So if the problem is in the white line......... opening any red line part will remove power from that line. Disconnecting a rollout switch opens the red line and kills the white line.

You have to go thru the white line circuit and look for a short. An ohmmeter would make that job easy.
 
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Old 12-22-19, 06:18 PM
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thank you so much for that explanation. it really helps a lot. I'm going to test everything with my meter and hope to find the issue. I handy but little experience with electrical circuitry
 
 

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