How to troubleshoot Nest offline?

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  #41  
Old 05-22-19, 09:48 PM
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No..... the furnace power is not needed for continuity.

I still can't figure out why both of them opened. It would mean the furnace would have to have been running very hot and even then the primary limit is supposed to reset automatically and the roll out switch gets reset by pushing the button. Sometimes due the age.... pushing the button doesn't do anything.

I hate to say it but it looks like both need to be replaced. If you want to test the system to be sure that is the only problem..... turn off the gas valve and temporarily connect pin 1 wire to pin 6 wire. Your stat should start working and the A/C should run.
 
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  #42  
Old 05-23-19, 05:54 AM
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Sometimes due the age.... pushing the button doesn't do anything.
Yes, I tried pushing a couple of times and it does not seem to budge at all.
I hate to say it but it looks like both need to be replaced.
You mean replace the Roll-Out switch and Limit Control? The Roll-Out switch seems easy to replace but the Limit Control seems a bit more involved.
...turn off the gas valve and temporarily connect pin 1 wire to pin 6 wire. Your stat should start working and the A/C should run.
So as a test, I should remove the plug and wire both pin 1 and pin 6 together only and the thermostat and A/C should work again, correct?

Thanks for all your help, PJmax, much appreciated for your help over the years.
 
  #43  
Old 05-23-19, 11:16 AM
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They are both easy to replace. Two screws and easily removable.

You can't remove the 6 pin plug from the board. You take the red wire that goes to pin 1 and the red wire that goes to pin 6 and touch them together. Use a small piece of solid wire to connect them.
 
  #44  
Old 05-23-19, 11:48 AM
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Okay, just to be sure I'm clear on this. I need to purchase and replace the Roll-Out switch and Limit Control, right? What part number should I be looking for? I think the board is Honeywell but the furnace is a Trane brand.
 
  #45  
Old 05-23-19, 12:44 PM
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That part don't have to be a specific brand but the values need to match.

The limit switch is a 36T01B3.
L180-20f means it opens at 180f° and closes at 160°f.

The rollout switch will have the temperature listed on it.
 
  #46  
Old 05-24-19, 09:12 AM
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Okay, so I remeasured once again and it seems the only that is bad (OL) is the 36T01B3 L180-20f limit switch. The one on the side looks fine. I measured zero. The question is, I couldn't one that is L180-20f. I found one that is L180-30f. Will it be fine if the new one is different by 10 degrees?
 
  #47  
Old 05-24-19, 11:42 AM
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L180-30f will be fine there.
Takes yours out and measure how far into the plenum the sensor is so that the new one matches.
 
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Old 05-24-19, 02:37 PM
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PJmax, I couldn't thank you enough for all the help you've done so far in this thread and many of my other threads. I took out the limit switch, called a local part supplier and he has an exact match. I just put in and it works! The fan did not automatically start when I switch on the furnace, which is a good thing. And yes, I got 24v on on the t-stat red wire. So, over all you've saved me at least $100+. I only paid for the part and best of all, I learned something along the way. So, many thanks for your help again.
 
  #49  
Old 05-24-19, 02:47 PM
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Good job . You hung in there.
 
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