Honeywell Home THP9045A1098 C-Wire Adapter — Installation Guide

Installation guide for the Honeywell Home / Resideo THP9045A1098 C-Wire Adapter, which provides a C (common) wire to power a smart thermostat when no C wire is already available.

Overview

This product creates a C wire (common wire) to power a thermostat. Only install it if you do not already have a C wire available to connect to your thermostat.

Zoned systems: for zoned HVAC systems, install the C-Wire Adapter between the thermostat and the zoning control panel — NOT between the zoning panel and the HVAC equipment.

Before You Begin

1. Turn off power at the breaker box or control switch for your HVAC (heating, ventilation, and air conditioning) system.
2. Remove your old thermostat from the wall plate. Do not remove any wires at this time.
3. Take a picture of the wiring, making sure the terminal labels and wires are both visible — you may need to reference this picture later.
4. Confirm you do not have a wire already in the C terminal. If you do, you don't need this product. Also look for any unused wire — if one exists, you don't need this product either; simply connect one end to the C terminal at the HVAC and the other to the C terminal at the new thermostat. Note: the C (common) wire may be labeled B rather than C on some thermostats.

At the HVAC Control Board

5. Go to your HVAC system (attic, crawl space, or basement) and open its cover to reveal the control board.
6. Take a picture of the wires on the control board, ensuring terminal labels and wires are visible. Note: the O or B terminal may also be used in place of W on some systems.
7. Use stickers to label the connected wires: G, C, R or Rc, W or W1, Y or Y1. If multiple wires are connected to a single terminal, label only the wire running to your thermostat. On heat pump applications, the wire from O/B on the old thermostat matches to O or B at the equipment rather than W.
8. Disconnect ONLY the wires you just labeled (G, R or Rc, W or W1, Y or Y1) — do not disconnect any unlabeled wires. If multiple wires share a terminal, remove only the one running to your thermostat.

Wiring the C-Wire Adapter

9. Insert the disconnected wires into the C-Wire Adapter terminals as follows — this converts the G and Y wires into C and K wires:

   Wire	Adapter Terminal
   W or O/B	W or O/B
   G	C
   Y	K
   R	R

10. Take a picture of the wires now inserted into the C-Wire Adapter, with terminal labels visible.
11. Connect the wires from the "Equipment" labeled side of the C-Wire Adapter to the matching terminals on the control board (C→C, R→R, W/W1/O/B→W, W2→W2, Y/Y1→Y). If there are separate wires to W and O, leave both attached at the HVAC and do not connect them to the C-Wire Adapter.
12. Checkpoint: the C-Wire Adapter should now be installed between your thermostat wiring and the HVAC control board (Thermostat → C-Wire Adapter → HVAC Control Board).

Mounting the Adapter

13. Before mounting, make sure the surface is clean enough for good adhesion. Attach the C-Wire Adapter to the inside wall of the furnace using the magnet on the back. (Note: earlier versions of this product used an adhesive pad and mount instead of a magnet.)
14. Close the HVAC system's cover. Leave the power off.

Labeling the Converted Wires

15. Go back to your thermostat location and label your now-converted wires: the wires you labeled C and K are the ones you inserted into the C and K terminals in step 9.
16. Label ALL of the remaining wires according to their terminals. The O/B terminal may also be used where noted.
17. Confirm you have labeled ALL of your wiring, then disconnect the wires from the old wall plate. (The O/B terminal may also be used.)

Next Steps

Refer to your new thermostat's installation guide for detailed instructions to complete the following:

1. Remove the old wall plate and mount the new one.
2. Wire the new thermostat, referring to the labels applied when inserting the wires. When wiring is complete, you should have wires in the C and K terminals — you should not have wires in the Y or G terminals.
3. Complete your new thermostat's installation by attaching the thermostat to the wall plate, restoring power, and configuring the thermostat.

Manufacturer

Resideo Technologies, Inc., 1985 Douglas Drive North, Golden Valley, MN 55422. 1-800-468-1502. www.resideo.com. Document 33-00618—03 SA Rev. 05-23. The Honeywell Home trademark is used under license from Honeywell International, Inc.; this product is manufactured by Resideo Technologies, Inc. and its affiliates.