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


GeniSys 7505 side view: Tw and Tr wires go to the Honeywell Thermostat


Honeywell Thermostat: red wire is connect to R + Rc and the white wire is connected to W


White Rodgers 90-113 fan controller


White Rodgers Wiring


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

 

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.

 

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:










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

 

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

 

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.

 

As an update: after doing some more research, I found that Beckett makes an add-on kit for the GeniSys 7505: the A/C Ready Kit (Part #51950U).
https://www.beckettcorp.com/product/ac-ready-kit/


I was able to attach the kit to my system, ran 120v power to it, and then connect the Nest with the new R, W and C wires.

Thanks for pointing me in the right direction, Pete! I appreciate the help!
Bruce

 

You're welcome and thank you for the additional information.

 

Hi Ber1983,

Do you have a pic of the before and after ready kit install? I have the same setup and just purchased the kit. Going to try over the weekend!

 

Welcome to the forums.

A very easy kit to install. The guide they give you is basically before and after.
I added an easy to follow wiring diagram for you.

Beckett install (pdf)

 

I also have a beckett 7505 trying to hook up a ecobee 4 WiFi thermostat would this setup also work for me . I don’t have a/c or fan, just a oil burning furnace . Only have two wires W and R missing C

 

Welcome to the forums.


You either need to add a 24vac transformer and a relay OR a fan center OR the Beckett kit.
The PEK kit that comes with the Ecobee should allow it to run in two wires but I don't recommend it.
I highly recommend running a new cable.