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What you will learn from How to Wire an Air Conditioner for Control - 5 Wires article:

  1. this article includes a comprehensive list showing thermostat wire terminations for an air conditioner and a source of heat that includes five wires.
  2. a detailed description of where each wire goes in the air handler and condenser and what it controls.
  3. a detailed diagram illustrating where the wires go for 5 wire air conditioner and heating system control.
  4. resource and related links to help you with wiring and installing a thermostat.

How to Wire an Air Conditioner for Control - 5 Wires

How to Wire an Air Conditioner for Control - 5 WiresHow to Wire an Air Conditioner for Control - 5 Wires  – The diagram below includes the typical control wiring for a conventional central air conditioning system. It includes a thermostat, a condenser, and an air handler with a heat source. The heat source for a basic AC system can include heat strips for electric heat or even a hot water coil inside the air handler that is fed from a water heater. Every conventional residential AC system uses 24-volts for the control of the system. All the relays in the system have 24-volt coils.

Circuit boards or printed circuit boards found in modern systems utilize 24-volt control which originates from the control transformer. Typical systems that do not use 24-volt control are window unit air conditioners, ductless mini split systems, and baseboard electric heating systems.

If you are unsure about the control voltage of your system consult an HVAC professional as some appliances use high voltage and this can be dangerous.
Related Link: Standard 18 gauge thermostat wire is used for all control wiring.(opens in a new window)

How to Wire an Air Conditioner for Control - 5 Wires - Thermostat Wiring Diagram

Air Conditioner Control - Thermostat Wiring Diagram - HVAC Systems

How to Wire an Air Conditioner for Control - 5 Wires - Breakdown of colors and terminals

  1. The R terminal is the 24-volt hot feed from the control step down transformer that will power the relay, contactor, or complete the circuit in the circuit board feeding it with 24 volts when the thermostat calls for whatever it is set for.
  2. The W terminal is for heating including the heating for gas furnaces, electric furnaces, boiler systems and the backup heat for heat pumps.
  3. The G terminal is the blower fan located in the air handler. It is the fan that circulates air throughout the ductwork system.
  4. The Y terminal is the terminal that will turn on the air conditioner and typically is terminated at the compressor contactor in the condensing unit located outside. It will be one of the few control wires (thermostat wires) that will terminate at the condenser in a split system air conditioner and heating system. Typically, the yellow wire will be ran to the air handler where at the air handler this wire is usually connected to another wire (typically by wire nut but could be connected via a terminal strip in the air handler) and then ran outside to the condensing unit along with at least one other wire in an air conditioner split system set up. The other control wire will be the common wire need at the compressor contactor where the coil in the compressor contactor needs a hot and a common from the control transformer to work.
  5. Finally, the C terminal is the common terminal and this terminal feeds the common side of the load from the control transformer.

Related Link: Control Circuits for Air Conditioning & Heating - Delve deeper and learn more about HVAC (opens in a new window)

Temperature Control, HVAC Thermostats, and HVAC Systems

Heating and cooling systems always require some kind of control. When you combine a home heating system with cooling equipment such as an air conditioning unit you will typically need a 5 wire thermostat to control the entire system with a single thermostat. This will not be the case with a heat pump system as they will require more wires for thermostat control. Therefore it is important that you know the type of system you have before replacing your thermostat. Furthermore, you can lower energy bills and energy cost by installing a smart thermostat or a programmable thermostat. Many digital thermostats available today are very forgiving in thermostat selection. Kind of like a one size fits all so a heat pump thermostat will be okay with an air conditioner and gas furnace combination. You will simply follow the instructions for wiring including color codes (the wire color code for thermostat control) and then the setup instructions.

Many manufacturers produce smart thermostats that will typically require a WiFi connection. Honeywell, Nest, Ecobee, Sensi and many others are available and can save in home energy costs. Use High Performance HVAC to install the new thermostat along with the manufacturer’s instructions and you will save energy. Getting rid of an old mechanical thermostat will definitely save you in the long run.

Terminal Strip where wire terminations are made during installation. Typically inside the air handler.

Terminal Strip in an Air Conditioner Air Handler - Electrical Connections

Additional resource links for wiring a thermostat:
1) Thermostat Wiring Colors
2) How to wire a thermostat
3) Heat Pump Thermostat Wiring Chart & Diagram
4) Select the Proper Thermostat for Your HVAC System

High Performance HVAC Technical Information

How to Wire an Air Conditioner for Control - 5 Wires

To learn more about heating systems and HVAC use this resource.

If you are purchasing new HVAC equipment don't forget to check out our HVAC Consumers Buyers Guide Category for lots of help.

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