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Adapt a 5-Wire Thermostat to a 4-Wire System
Venstar ACC0410 Add-A-Wire Accessory for Programmable Digital Thermostats
Venstar ACC0410 Add-A-Wire Accessory for Programmable Digital Thermostats
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Add-A-Wire Dimensions 4 to 5 Wire Thermostat Diagram 2 Wire Cooling & Heating Diagram
4 Wire Single Stage Heat Pump Diagram
Venstar ACC0410 Add-A-Wire Accessory for Programmable Digital Thermostats
Item# 304AAW
Price: Normally $35.99 
Hot Deal $22.50
Free shipping on orders over $175 - See Details


  • Allows 5-wire thermostats to use only 4 wires
  • Also allows 5 wires to work like 6 wires
  • Use it to fix a broken wire
  • Add cooling to a heat only system
  • Easier than running new wire

Essential Info

In applications where additional wiring cannot be run to your programmable digital thermostat, the Add-A-Wire accessory can be used to add a wire to the thermostat. The accessory can also be used for fixing a broken wire, to make one thermostat work like two, to add cooling to a heat-only system, or to add a common wire to a 4-wire system.

Please note that the green and yellow wires of the Diode "Y" may not be connected to the R or C terminal of the thermostat. (The function of a diode is to allow current in one direction and to block current in the opposite direction.)

This accessory works with the Venstar 1-Day Programmable Digital Thermostat, the 7-Day Programmable Digital Thermostat, and the 7-Day Programmable Thermostat, Dual Fuel (each sold separately).


What's Included

  • 1x - Add-A-Wire Accessory
  • 1x - Y Diode
  • 4x - Wire Nuts
  • More Info

  • Includes Yellow, Green, Blue wire splice (directionally sensitive)
  • Includes 4 wire nuts
  • Wires running from Add-A-Wire accessory are 9 inch long
  • Maximum distance for Add-A-Wire using 18-gauge wire is 100 feet
  • Makes one wire work like two
  • Mounts inside equipment (not for outdoor use)
  • For use with 24-volt HVAC systems
  • Cannot be used as "R" power or "C" common wire

  • Specifications


    Manufacturer Product No.:ACC0410
    Dimensions:3" x 1.75" box and 9" long wires
    Weight:0.5 lb.
    Safety Approvals:UL Listed
    Regulatory:FCC Compliant
    Warranty:5 years, limited

    Important notes:
    Defective exchanges for identical item within 30 days of purchase. After 30 days, please contact the manufacturer.
    Manufacturer contact information: US Air Conditioning Distributors, Tel: (626) 854-4555


    Add-A-Wire Dimensions  4 to 5 Wire Thermostat Diagram  2 Wire Cooling & Heating Diagram  4 Wire Single Stage Heat Pump Diagram 
    Add-A-Wire Dimensions  4 to 5 Wire Thermostat Diagram  2 Wire Cooling & Heating Diagram  4 Wire Single Stage Heat Pump Diagram 


    50 Ratings
    5 star: 42%  (21)
    4 star: 24%  (12)
    3 star: 22%  (11)
    2 star: 2%  (1)
    1 star: 10%  (5)
    Average Customer Rating
    (50 customer ratings)
    Share your thoughts with other customers
    STEVEN -- rochester, MI   2/13/2014
    Sure beats running an extra wire.
    Gus -- United States   1/25/2014
    I was actually surprised to find a device that solved exactly the problem that I ran into when trying to install a new thermostat. The instructions were clear. Installation was straight-forward. The box part fits easily in my HVAC unit. The diode part fit nicely inside my thermostat. After carefully following the instructions and planning my wiring diagram, it worked perfectly on the first try. Nice!
    Mike C -- san diego, California   1/23/2014
    What a great device. It works exactly as described. My particular wiring at the furnace was a little different than expected. But common sense, and a few questions in the smarthome help forum, made this an easy install. I was able to add a new honeywell wireless thermostat AND still keep my independent control to turn the fan-only on when ever I want to. I would recommend this to any DIYer who is comfortable with doing wiring.
    JC3 -- clinton twp, MI   1/9/2014
    Works great!
    THOMAS -- minneapolis, MN   1/2/2014
    Fast shipping. Exactly what I ordered. Add-a-wire saved me hours of work pulling a new thermostat wire.
    RICHARD -- portland, OR   12/6/2013
    Works as advertised. Definitely easier than running new wires.
    THOMAS -- chicago, IL   11/29/2013
    didn't need it as I discovered two additional wires that were hidden
    BRIAN -- vernon hills, IL   11/21/2013
    Quick service, great price and easy to install.
    PATRICK -- windsor, ON   11/4/2013
    Does what it needs to providing that 5th wire so needed now on the newer thermostats.
    STEPHEN -- singer island, FL   9/5/2013
    This was a real life-saver. We wished to replace two battery-operated t-stats with Z-wave compatible programmable t-stats, but the existing wiring was four-wire cable. These boxes saved us a lot of time and money by relieving us of the need to cut drywall and rerun t-stat wiring. Has worked very well in the weeks since we installed them.
    SAMMYE -- denver, CO   7/19/2013
    Works exactly as it should. Directions are not the clearest, but experience with electronics made it easy. Allows you to free up one wire, which you use for the C wire.
    JOERG -- newtown, PA   6/22/2013
    installation was very easy, allowed me to use the new Thermostat without pulling new cable from furnace to thermostat. Great product!
    Amarks -- St. Louis   2/24/2013
    Outstanding product! Works without a flaw. A must need if you have vacation property.
    PATRICK -- winnipeg, MB   12/24/2011
    Haven't installed it as I am waiting for a few more pieces to arrive to complete this task. I am sure it will be fantastic as others have mentioned.
    JONATHAN -- toronto, ON   9/22/2011
    Fantastic product - so much easier than pulling a new wire. Works as advertized. Good applications: Adding common wire, upgrading to a 2-stage t-stat, fixing broken conductor. Warning: A good background of hvac control circuits is required to install this product correctly. If you know what each thermostat wire does, call an hvac technician.
    ij_20 -- Ontario   9/1/2011
    Good product. Warning: If you're not familiar with hvac control wiring, don't buy this - call a technician.
    olsonbri -- san diego, California   7/15/2011
    Very poor documentation. I wanted to add a common wire to a 4 wire setup. No examples of this, and the examples that are there are confusing i.e., they show an example of a 4 wire setup to add a 5th wire, but in the illustration there are 5 wires coming from the HVAC. Will return.
    LONNY -- moorpark, CA   7/7/2011
    Worked perfectly for my need
    DAVE -- calgary, AB   1/14/2011
    Excellent. Arrived on time.
    fl homeowner -- ft. myers, FL   1/11/2011
    I am needing to add a common wire, as our builder did not hook it up at either end,battery thermostat was used can hook to thermostat, but cannot find other end at air handler to try. Would this product work for us? We need help!!! I don't wan to return our new thermostat!!!


    1-day Programmable Digital Thermostat  7-day Programmable Digital Thermostat  7-day Programmable Thermostat, Dual Fuel  Venstar Extra-Zone for Venstar Thermostats 
    1-day Programmable Digital Thermostat  7-day Programmable Digital Thermostat  7-day Programmable Thermostat, Dual Fuel  Venstar Extra-Zone for Venstar Thermostats 

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