A common wire (C) is required for 5-wire thermostats. If there are only 4 wires to your existing thermostat (i.e. there is no C wire), you can use the ecobee Power Extender Kit to power your thermostat.
Step 1. Install Wiring Harness
The Power Extender wiring harness must be installed in an indoor, dry location, near the HVAC equipment. When choosing a location, the distance between the wiring harness and the HVAC equipment must not exceed 24 inches (0.6 m) .
This equipment is sensitive to electrostatic discharge (ESD). Before starting, discharge your body of static electricity by touching a grounded metal object. Always hold the devices by their edges and do not touch any of the internal components.
1. Power off the HVAC equipment.
2. Remove the top cover of the wiring harness by gently squeezing its sides.
3. Use 2 #6 pan-head screws or double-sided adhesive to attach the wiring harness to a flat surface (for example, the furnace casing).
Step 2. Install Diode
The diode is designed to be installed behind the thermostat, within the thermostat’s backpanel wire opening.
1. Use your fingers to gently pry the thermostat away from its base.
2. Using the thermostat’s backpanel wire opening as a guide, gently bend the diode wires 90 degrees so that they can be inserted into the W O/B and Y terminals:
The diode itself should stay within the wire opening.
3. Clip the diode legs so that you can insert them into the W and Y terminals. DO NOT over clip the legs.
4. Connect the diode legs to the W O/B and Y terminals.
Step 3. Connect the Wires
The next step is to connect the wires between the thermostat, diode, wiring harness, and HVAC equipment.
1. Connect the C wire coming from the thermostat to the C terminal on the STAT side of the wiring harness. You can repurpose the wire that would have been connected to W on a 4-wire thermostat.
2. Connect the RC/RH and G wires from the thermostat to the RC/RH and G terminals on the STAT side of the wiring harness.
3. Connect the output from the diode to the Y terminal on the STAT side of the wiring harness. You can re-use the wire that would have been connected to Y on a 4-wire thermostat.
4. Connect the RC/RH, G (fan), Y, C, and W wires on the EQUIP side of the wiring harness to the matching terminals on your air hander.
Step 4. Power On the System
After you have completed the wiring, you can power on and test the system.
1. Re-attach the thermostat to the backplate. Ensure that the pins on the thermostat align with the terminal block on the backplate.
2. Power on the HVAC equipment. The thermostat should automatically power on.
3. Test your wiring by alternately adjusting the set temperature and running the different heat, cool, and fan modes.
4. Once you are satisfied the wiring is correct, re-attach the wiring harness’s front cover. Make sure the wires exit the module via the wire channel.
5. Re-attach any cover panels that you previously removed on the HVAC equipment.