C-wire from AC in two transformer setup

Users who are viewing this thread

johnlo23

New Member
Messages
2
Reaction score
0
Points
1
Location
New York, NY
I have six wires going to my thermostat. Only five are used.
I need to connect my Blue wire to Common 24V to power my new Honeywell RTH8580WF1007 Wifi thermostat.

With the old thermostat, this is the wiring:

First transformer, only two wires:
Heat White - W
Heat Red - Rh


Second Transformer:
AC White - Y
AC Red - Rc
AC Green - G


The AC transformer has an unused C terminal. Both transformers are hard-wired units.

This is the diagram of the Honeywell:
upload_2017-9-14_17-22-51.png


Can I hook up like this:
Rc to Rc
Rh to R
W to W

Y to Y
G to G
C to C

Will the Thermostat get power from C on the AC transformer? Do I leave the RC-R Jumper connected or remove it?
 

Reach4

Well-Known Member
Messages
38,798
Reaction score
4,412
Points
113
Location
IL
I think you should check further, but my thinking is that you do as you suggest.

Then hook Heat White - W and AC White - Y both to C on the transformer. But I am not sure. Verify independently.
 

WorthFlorida

Clinical Trail on a Cancer Drug Started 1/31/24. ☹
Messages
5,727
Solutions
1
Reaction score
982
Points
113
Location
Orlando, Florida
Why two transformers? Do you have a separate furnace and AC system? Two stage heat?

The Rh would be from the heating system transformer, Rc from the cooling system transformer with the jumper removed with two separate systems. If your spare wire is a blue or black use that for the c wire.
 
Last edited:

johnlo23

New Member
Messages
2
Reaction score
0
Points
1
Location
New York, NY
Why two transformers? Do you have a separate furnace and AC system? Two stage heat?
Yes. Heat is hot water from the oil burner. A/c is forced air system. The transformers are on opposite sides of the basement.
After reading more, I think the thing I thought was the AC transformer is a transformer / relay combo that switches the AC fan and compressor on.
 
Last edited:
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks