Air conditioning condensing units communicate with the furnace via two thermostat wires. The two wires are encased in insulation to make one two-wire thermostat wire. One of these wires runs from the air conditioning condensing unit to the furnace. The main thermostat wire then runs from the furnace to the thermostat. Wiring your A/C thermostat with two wires is actually the among easiest steps in installing an air conditioning condensing unit.
Things You'll Need
- Tape measure
- Thermostat wire
- Wire stripper
- Wire nuts
- Zip ties
Turn off the power to the furnace and air conditioning condensing unit by turning off the correct circuit breaker in the circuit breaker panel.
Install a two-wire thermostat wire from the air conditioning condensing unit to the furnace. Strap it to the copper line sets that run from the furnace to the condensing unit with zip ties.
Strip about 2 inches of the outer layer of insulation back on the thermostat wire at both the condensing unit and the furnace to expose the two wires inside. Strip each of these wires back 1/4 inch to expose the bare copper.
Connect the red and white wires of the thermostat wire to the red and white wires coming from the condensing unit with wire nuts.
Connect the red thermostat wire to the "C" terminal on the furnace control board. Connect the white thermostat wire to the "Y" terminal on the furnace control board.
Check to see that the yellow wire coming from the thermostat is connected to the "Y" terminal on the furnace control board also. If it isn't, connect it.
Go to the thermostat and remove it from the wall by applying gentle pulling pressure. Check to see that the yellow wire is connected to the "Y" terminal. If it isn't, connect it.
Push the thermostat back on to the wall plate by pushing with gentle pressure until it snaps into place. Turn the power back on to the furnace and air conditioning unit. Set the thermostat to your desired setting and your air conditioner should function properly.
Tips & Warnings
- Make sure the power is off to the furnace and air conditioning unit. Failure to turn the power off could result in a severe electrical shock.
- High Performance HVAC: Thermostat Wiring Colors
- Timothy Gonyo; Sheet Metal Workers Local #18; Milwaukee, Wisconsin
- Photo Credit Jupiterimages/Creatas/Getty Images
How to Connect Thermostat Wiring
Putting in a digital thermostat helps control your heating and cooling bill and maintains a more even temperature throughout your home. You...
How to Wire a Honeywell Thermostat
Your programmable Honeywell thermostat can help you save up to 33% on your utility bill. It adjusts the temperature up and down...
How to Wire a Thermostat
Your common electronic programmable thermostat operates off four wires to control both the heater and the air conditioning unit. When you wire...
How to Wire a Furnace Thermostat With 2 Wires
The simplest setup for a heating system is a thermostat that is wired with two wires. In order for a thermostat to...
How to Troubleshoot a Two Wire Thermostat
In time, your heating system may begin acting erratically. If it suddenly stops working properly, the problem may either be in the...
How to Install a Two Wire Thermostat
Depending on the heating system you have, you can have from two all the way up to eight wires that run from...
How to Wire an Outside AC Condenser
An air conditioning system uses the outside condensing unit to force liquid refrigerant through a metering valve, found in the inside unit's...
How to Wire a Furnace Transformer
A transformer links a furnace's high-voltage and low-voltage circuits together. The transformer gathers its high-voltage power supply from wires that connect to...
How to Wire an Air Conditioning Thermostat
Air conditioners are activated through the use of a thermostat. Older houses used mercury switches but modern construction uses digital thermostats. Installing...
How to Wire a Ruud Thermostat
Wiring most thermostats is done in the same manner with minor exceptions depending on the brand and what the specific unit was...
How to Wire an AC Thermostat in an RV
In common with most coach accessories in an RV, the thermostat that controls the air conditioner (AC) is a regular household unit....
How to Wire the Thermostat to a Comfortmaker
Comfortmaker manufactures gas and oil furnaces, heat pumps and air conditioners. It is one of seven brands of International Comfort Products Corporation....
How to Read HVAC Wiring Diagrams
If you are unfamiliar with the process of reading HVAC, or heating, ventilation, and air conditioning wiring diagrams, then fixing your own...
How to Wire an RV Thermostat
Coach thermostats in recreational vehicles, or RVs, fulfill the same purpose as thermostats in regular "sticks-and-bricks" houses. They control the output of...
Intertherm Air Conditioner Wiring
Intertherm is a brand of the Nordyne company. The Intertherm brand produces a limited number of products, including split systems. Split systems...