Page 1
C-WIRE ADAPTER
1
Turn the power off at the
breaker box or control
switch for your HVAC*
OFF
system.
ON
Go to your HVAC system. It may be located in your
attic, crawl space or basement.
5
Open HVAC system’s cover
to reveal the control board.
Installation Guide
Online Guides and Support
resideo.com
M38945
33-00618-03
Overview
This product provides a C wire (common wire) to power a
thermostat. Only install if you do not have a C wire available to
connect to your thermostat.
ZONING CONTROL PANEL CHECK
For zoned systems, install the C Wire Adapter
between the thermostat and the zoning panel, NOT
between the zoning panel and HVAC equipment.
BEFORE
HVAC
Thermostat
2
3
Breaker box
CWW2GRKY
OFF
Switch
*Heating, ventilation, and air conditioning
Remove your old thermostat
from the wall plate.
Do not remove any wires
at this time!
M38949
Take a picture of the wiring.
Ensure the terminal labels
and wires are in the image.
CWW2GRKY
Wires
Terminal Labels
You may need to reference
the picture later.
M38950
M38948
M38952
6
G
C
R
W
*
W2
Y
7
**
G
R
W
Y
EXAMPLE
G
C
R or Rc
W or W1
W2
Y or Y1
M38954
Take a picture of the wires
on the control board.
Ensure the terminal labels
and wires are in the image.
You may need to reference
the picture later.
O or B terminal may also be used.
*
M38953
Use stickers to label the
following connected wires:
G
•
R or Rc
•
Not all systems will have a
*
W or W1-wire. On a heat pump
application, the wire coming from
*
O/B on the old thermostat would
match to either O or B at equipment
rather than W.
If multiple wires are connected
**
to a terminal, only label the the wire
running to your thermostat.
W or W1
•
Y or Y1
•
Thermostat
AFTER
C-Wire
Adapter
HVAC
M38946
M38947
4
C
C terminal
*
M38951
Confirm that you do not have
a wire in the C terminal. If
you have a wire in the
C terminal, then you do not
need this product.
Look for an unused wire. If
you have an unused wire,
then you do not need this
product. Connect one end of
that wire to C terminal at the
HVAC and the other to C
terminal at new thermostat.
The C wire (common) might be
*
labeled as B rather than C on certain
thermostats.
8
*
**
EXAMPLE
G
R
W
Y
G
C
R or Rc
W or W1
W2
Y or Y1
Disconnect ONLY the wires
that you just labelled:
G
•
R or Rc
•
Do NOT disconnect wires that you
*
did not label.
If multiple wires are connected
**
***
to a terminal, only remove the the
wire running to your thermostat.
On a heat pump application,
***
the wire coming from O/B on the old
thermostat would match to either O
or B at equipment rather than W.
M38955
W or W1
•
Y or Y1
•
CONTINUE
Page 2
9
10
Insert the wires you just
13
disconnected into the
C-Wire Adapter terminals.
Wires
W or O/B
G
Y
R
Terminals
W or O/B
C
K
R
R
G
Y
M38956
This will convert the G and
Y-wires into C and K-wires.
Before mounting, check to
make sure surface is clean
enough to ensure good
adhesion.
Attach the C-Wire Adapter to
the inside wall of the furnace
using the magnet on the back
of the C-Wire Adapter.
Note: Earlier versions of this
product had an adhesive pad
and mount rather than magnet.
M39008
17
C
W
*
18
NEXT STEPS
EXAMPLE
R
Confirm you have labelled
ALL of your wiring.
Disconnect the wires from
K
the old wall plate.
O/B terminal may also be used.
*
M38964
Refer to your new thermostat’s
installation guide for detailed
Take a picture of the wires
you inserted into the C-Wire
14
Close the HVAC system’s cover.
instructions to complete the
following tasks below.
Adapter.
Ensure the terminal labels
and wires are in the image.
You may need to reference
WC K
R
G
W
G
G
R
Y
Y
M38957
the picture later.
M38961
Leave the power off.
M38965
A
Remove the old wall plate and mount the new one.
11
G
12
CHECKPOINT
EXAMPLE
C
R
W
Y
G
C
R
W, W1 , O, or B
W2
Y or Y1
Connect the wires from
the “Equipment”
labelled side of the
C-Wire Adapter to the
matching terminals on
the control board.
If there are separate wires to
*
*
W and O, leave the W and O wires
attached at HVAC and do not
connect them to the C-Wire
Adapter.
M38958
Your C-Wire Adapter should now be installed between
your thermostat wiring and the control board.
Thermostat
C-Wire
Adapter
Control Board
HVAC
M38959
Go back to your thermostat.
15
C
G Y
16
EXAMPLE
C
W
*
G WRY
M38966
B
Wire the new thermostat.
Label your now converted
wires as shown.
K
G
Y
Wires
The wires you label C and K are
the wires you inserted into the
M38962
C and K-terminals in step .
Label ALL of the remaining
wires according to their
terminals.
O/B terminal may also be used.
K
R
*
M38963
Labels
C
K
W
C
W
K
R
K
R
M38967A
C
9
C
Complete your new thermostat’s installation by
attaching the thermostat to the wall plate,
restoring the power, and configuring the
thermostat.
Resideo Technologies, Inc.
1985 Douglas Drive North, Golden Valley, MN 55422
1-800-468-1502
www.resideo.com
© 2023 Resideo Technologies, Inc. All rights reserved.
This product is manufactured by Resideo Technologies, Inc. and its affiliates.
The Honeywell Home trademark is used under license from Honeywell International, Inc.
This product is manufactured by Resideo Technologies, Inc. and its affiliates.
33-00618—03 SA Rev. 05-23 | Printed in United States
Refer to the labels you
applied when inserting
the wires.
When done wiring, you should
have wires in the C and
K-terminals.
You should not have wires in
the Y or G-terminals.
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