Honeywell WiFi TStat Upgrade

Old 06-09-14, 08:41 PM
Thread Starter
Join Date: Jun 2014
Posts: 5
Received 0 Votes on 0 Posts
Honeywell WiFi TStat Upgrade

Attempting to upgrade from a old battery operated digital Tstat to a Honeywell Wifi Tstat. New Honeywell system requires "C" 24VAC input.

Here's my situation.
Wire bundle running to Tstat is 4 wires (blue, red, white, green), no common.
Honeywell wiring option video suggests moving green wire to "C" both at Tstat and furnace terminal block, then jumping "Y" and "G" at furnace. I lose independent control of fan, but no biggie.

My complexity is I have a second wire bundle running from what I believe is interruptable electric service that controls my air conditioning into the furnace terminal block. The bundle has 3 wires - white, red, green - that were wired into the furnace terminal block before this upgrade attempt.

Before messing around with furnace terminal block, white was on the "Y" cooling terminal, red was on "R", and green was on "G" fan terminal. Can I wire these in and keep interruptible air conditioning?

I'm very close to calling an HVAC pro, but figured I throw it here first. Pics below. 4 wire bundle from Tstat is coiled in yellow wire near terminal (yellow wire does NOT run back up to Tstat, so cannot be used as common)

Name:  photo (1).jpg
Views: 587
Size:  24.3 KBName:  photo.jpg
Views: 541
Size:  31.9 KB
Old 06-09-14, 08:49 PM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 7,425
Received 17 Votes on 14 Posts
Your picture shows an available yellow wire that you can use for common.
Is this yellow wire also at the stat?
Old 06-10-14, 04:28 AM
Thread Starter
Join Date: Jun 2014
Posts: 5
Received 0 Votes on 0 Posts
no yellow wire @ Tstat. The 4 wire bundle is spliced to 5 wire inside furnace cabinet as shown.

My simple mind thinks the following configuration should work. Thoughts?
4 wire from Tstat
red -> "R"
white -> "W"
blue -> "Y"
green -> "C" (lose independent fan control)

3 wire from AC unit
red -> "R"
white -> "Y"
green -> "G"

Name:  photo.jpg
Views: 485
Size:  42.1 KB

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: