Connect Nest Thermostat E to Genisys 7505 oil burner

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  #1  
Old 02-09-19, 04:24 PM
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Connect Nest Thermostat E to Genisys 7505 oil burner

Hello!

I currently have an oil furnace that uses a GeniSys 7505 120v burn control that is connected to a Honeywell round basic thermostat with 2 wires (Red and White). I wanted to upgrade to a Nest Thermostat E, so, I turned off the furnace and swapped out the thermostats. When I powered the furnace back up, the Nest began booting, but, I could hear the furnace "pulsing". After doing some research, I came to the conclusion that I need to add a C wire to provide more power. After looking a bit more into the furnace, I see there is a White Rodgers 90-113 fan controller in it, which has a C wire on it. Can I just run a wire from that C terminal on the fan controller to my thermostat and get power for the Nest? Or is there more involved?

GeniSys 7505 top view
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GeniSys 7505 side view: Tw and Tr wires go to the Honeywell Thermostat
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Honeywell Thermostat: red wire is connect to R + Rc and the white wire is connected to W
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White Rodgers 90-113 fan controller
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White Rodgers Wiring
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I noticed while posting this, the white and red wires are in my mind "swapped" on the furnace: the White wire is connected to Tr post, while the Red wire is connected to the Tw post. This is the way the wires have been for a long time: does it not matter which is connected to which, I take it?

Thanks for your help!!
Bruce
 
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  #2  
Old 02-09-19, 06:15 PM
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Welcome to the forums.

In my opinion..... a nest E is not directly compatible with your TT system.
You need a thermostat with an Rh and Rc like the regular nest.
That fan center has nothing to do with the burner control. That C on it is not a C for the two TT terminals.
You could use a full size nest and four wires or a 24vAC power supply at the nest itself.

Actually if you have three wires from the furnace to the stat..... you could use a 24vAC relay or the fan center relay to directly control the burner. If you'd like to use the fan center..... turn the power off, take the plate off and post a few pictures of the wiring.

That doesn't look like a three wire thermostat cable.
 
  #3  
Old 02-10-19, 09:19 PM
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Hello Pete. Thank you for your reply!

So much for things being easy! When you say I can use a 24vAC relay or the fan center relay: do you mean with this Nest E thermostat, or, would I have to get the Nest 3? I was hoping to use this one, as I only paid a little over $100 for it vs $249 for the Nest 3, but, if I have to get a Nest 3, I will.

Here's some pictures of the Fan Center wiring:

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I have some 18/5 thermostat wire that I'm going to replace the 2 wire with, so, that wiring shouldn't be an issue.

Thanks Again!
Bruce
 
  #4  
Old 02-10-19, 09:40 PM
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Your pictures are excellent. We can do what we need. I'll be back later to explain it.

This is so weird. Working with two members at the same time with similar equipment. In the other thread the member has the same seemingly unused fan center.

https://www.doityourself.com/forum/h...edom-80-a.html
 
  #5  
Old 02-10-19, 10:06 PM
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Wow! That's crazy: the furnace pictured in post #10 of that thread looks almost exactly like mine! I have a Trane XP80, although it appears the insides are shared between companies.
 
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