How To Wire An Air Conditioner To A Furnace & AC [Step By Step Guide]

To get your HVAC system working just right, you need to connect different parts of the system. Air conditioning involves both cooling and heating, so you may want to wire it up to a furnace and AC. But how should you do this? We have put together a step-by-step guide based on our research to help you!

To wire an air conditioner to a furnace, you will need access to the wiring systems of your furnace, thermostat, and outdoor condenser. Here is a brief overview of the steps:

  1. Prepare your equipment
  2. Turn off the main circuit breaker and ensure no power is running to any of the units
  3. Access the control panel of your thermostat
  4. Connect the appropriate color-coded wires from the furnace to the thermostat and outdoor condenser
  5. Connect the C-wire with your thermostat and HVAC system 
  6. Replace any removed panels and restart the power

Wiring your furnace to an air conditioner and AC is a way to combine heating and cooling systems. You can only do this on a forced-air system, which typically uses heat pumps. Keep reading to learn more about this and get detailed steps on wiring your air conditioner and furnace!

How To Wire An Air Conditioner To A Furnace & AC

furnace thermostat installation wire plate

Before wiring any of your units, make sure they are compatible with each other. In some cases, you may have to replace your entire air conditioning system to make sure it will work correctly. Furnaces and air conditioners are completely separate units, but they work based on the same mechanisms.

Modern thermostats are equipped to handle both heating and cooling. Having one is important for controlling which unit will turn on after you wire everything together. These instructions can help with wiring AC systems to thermostats like Nest, Honeywell, and Ecobee, among others.

Click here to see this smart thermostat on Amazon. 

1. Prepare Your Equipment

Have all the tools you need on hand when you set to work. This includes screwdrivers, extra screws and wires, electrical tape, and unit instruction manuals. If you purchase a new heating, cooling, or control unit, you can refer to the manual to help you with wiring.

You may need more or less equipment depending on your system. Otherwise, just a screwdriver will do. If you are not confident in your ability to wire an air conditioner to a furnace and AC, ask someone to help you or hire a professional.

2. Turn Off The Main Circuit Breaker

Before starting, you will want to turn off the power source of your HVAC system. Make sure that your units are powered off, as well. Leaving them on may damage the appliances and cause injury. 

3. Access The Control Panel Of Your Thermostat

Your furnace will have wires that you need to hook up to your thermostat. Access the control panel on the model you have. Double-check to see if all the wires are available.

4. Connect The Color-Coded Wires

Most furnaces have five wires, but your thermostat may have six or more. This is for connecting to the air conditioner. Here are the color-coded wires you will find:

  • W (white) for heating
  • G (green) for fan control
  • Y (yellow) for air conditioning
  • R (red) for the 24-volt feed
  • C (blue, sometimes white) control or common

On the thermostat, you may find two red terminals: one for cooling and one for heating. On the outdoor condenser, you will have a Y terminal and a C terminal. Connect the opposing ends of the wires to the appropriate terminals on your furnace, air conditioner, and outdoor condenser.

Click here to see these thermostat wires on Amazon.

5. Connect the C-wire between your thermostat and HVAC system 

If you have a modern or smart thermostat, connect the C-wire between the thermostat and your unit. This helps supply your thermostat with a constant stream of power. It also supports better compatibility in your system.

6. Replace any panels and restart the power

Now that everything is in place, you can cover any open panels and restart the power. Be sure to test out your HVAC system. If everything is working fine and you don't see any issues, then you have successfully wired your air conditioner to the furnace and AC!

Why Wire An Air Conditioner To A Furnace & AC?

hvac air conditioning unit on concrete

Wiring your furnace to the AC helps with temperature regulation in your home. Your thermostat or regulator will be able to switch between heating and cooling this way. Since most systems run on similar vents, ducts, and condenser units, a furnace and air conditioner cannot run at the same time.

Aside from ease of control, a central air conditioning system can also be more energy efficient. Your HVAC system will not have to work as hard to heat and cool your home if the furnace can raise its heat or use the fan as your thermostat runs.

Depending on the model of your thermostat, you may be able to control your home's temperature remotely. Smart technology allows you to access your HVAC controls so long as the wires are connected properly, and your system is configured via wi-fi.

How To Maximize Heating And Cooling

Some thermostats have an eco-saver mode that manages your HVAC system for you. If not, you can still save energy by configuring your thermostat manually. For example, do not set the temperature at extreme levels. Base the heating or cooling depending on the outside temperature for less exercise.

Do not make constant temperature changes, either. This can affect system performance as your furnace or air conditioner will be constantly adjusting. Take some time between temperature and settings changes for the sake of unit maintenance.

Why Are My Furnace And Air Conditioner Running At The Same Time?

technician heater issue caucasian worker looking

If your furnace and air conditioner are running at the same time, this will overload your HVAC system and cause problems. Incorrect wiring is the main reason this happens. Incompatible units could also lead to this issue.

When your AC and furnace are working at the same time, you should troubleshoot the system immediately. Chances are that you can quickly resolve this issue through some rewiring. Double-check your system specifications to make sure you are doing it right.

Also, make sure that each wire is connected to the correct unit, like the cooling wires to the cooling system and the heating wires to the heating system. Check for any issues with the units themselves and the configuration of your thermostat.

If you find yourself at a loss, call an HVAC technician. A professional will be able to help you pinpoint the problem and prevent it from happening again.

Do The Furnace And The Air Conditioner Use The Same Blower?

The furnace and air conditioner in an HVAC system use the same fan or blower. You might mistake this as both units running at the same time, but this is not the case. Rather, the same infrastructure is used by either machine to blow air through your house. This will either be cooled air or hot air.

Furnaces and air conditioners operate independently. They may be controlled by the same thermostat system and use the same condenser, vents, and fan, but that is the extent of the system. This is why you have to ensure all the parts of your HVAC system are compatible with each other.

Some furnaces can offer cooling without an air conditioner. The furnace fan can blow cooled air in or hot air out but will not cool the same way as an air conditioner. For the most part, you can use your furnace for its air distribution.

A furnace will send warm air through the fan from your heat pump or boiler. In contrast, when it comes to cooling, the air conditioner coil is positioned close to the fan. This distributes the colder air throughout your house.

How Long Can A Furnace And An AC Last?

HVAC heating air conditioning residential units, How To Wire An Air Conditioner To A Furnace & AC [Step By Step Guide]

As with most appliances, the average lifespan of an HVAC system is 10 to 20 years. You can get the most out of your furnace and air conditioner through proper maintenance and care, as well as regular repairs.

Some units can last 25 to 30 years. A furnace will last longer than an air conditioner. If only one of the units needs replacing, you might have to replace both if enough time has passed. However, you should still check the compatibility between an old unit and a replacement just to be sure.

When it comes to expenses, heating costs more. Furnaces also get more inefficient over time, so it is probably a good idea to replace your heating system at the 15- or 20-year mark. With regular use, it is unlikely that your entire HVAC system will last up to 30 years.

Wrapping Things Up

HVAC heating air conditioning residential units

Wiring an air conditioner to a furnace and AC involves connecting the entire HVAC system. With a modern thermostat, like an electric or battery-powered one, wiring units together is straightforward and relatively easy. Simply follow the color codes and hook up wires to the correct units.

Make sure to practice proper safety procedures when wiring. Also, take care not to wire the wrong terminals together, as this could lead to issues in the system and cause damage.

There are many types of heating and cooling systems, so you have to prioritize compatibility between your units. Forced air is typically used when combining systems.

Did you find this post helpful? If you did, check out our other articles before you go!

Daikin Vs. Rheem Furnace: Which Brand To Choose?

Where Is The Fuse In A Spilt Air Conditioner?

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