If you have only two wires available, yes. Otherwise, you will need to disconnect the fan+furnace wire bonding, and use them manually each time. Verify that the cable ran to the box does not have any additional wires in the sheath… If not, you’ll need to pull new wires through.

Is G wire necessary?

As you mentioned, you don’t usually need a G wire for heating mode, but you do for cooling. In special circumstances a relay could be wired up inside of the air handler to make the fan come on with a call for cooling, but normally it’s the thermostat that makes the connection that makes the fan come in in cooling mode.

Is it OK to just run the fan on the furnace?

Running your furnace fan all the time isn’t exactly a bad thing. In fact, there’s no need to worry about the fan wearing out or breaking down because it’s designed to run continuously, and there’s an array of benefits connected to this. Here are some of them: Better circulation of heated and cooled air.

What does the G wire at the thermostat control?

G: The G terminal controls the fan relay and is responsible for turning the blower fan on and off automatically or manually via the thermostat.

Can I run the fan only on thermostat?

You can run your system’s fan independently of heating or cooling. So your system doesn’t need to be actively heating or cooling to run the fan. However, you can only run the fan when your thermostat is set to a temperature mode (like Cool mode, for example).

Is it OK to substitute G wire for C wire?

Quote from the video:
Quote from Youtube video: Option you may know it as a wire that looks like this known as a jumper wire note if you have a jumper wire between our and our C terminals. Next use the supplied. City tags to label each wire.

How do you wire a furnace thermostat to heat only?

Quote from the video:
Quote from Youtube video: For that and these are very easy to install there are two wires. So when you remove the old thermostat. You're going to match up the wire that goes to the RH. And then the wire that goes to the W.

Does running furnace fan bring in outside air?

Whenever the fan runs, some ambient exterior air (hot/humid/cold/dry) will be mixed into the circulating air in your system.

Can you run a fan without AC?

Running It Without the AC Isn’t Always Efficient

Professional air conditioning repair technicians actually advise against this, however; while it’s true that the fan alone uses less energy than the AC, it will almost certainly result in higher utility bills.

Should I run my furnace fan all the time in the winter?

Furnace fans are designed to run all the time, so there’s no need to worry about it failing prematurely. Much of a furnace fan’s wear and tear comes from the starts and stops of the motor; keeping it running can eliminate this type of stress.

What wire controls the fan on the furnace?


Some of the other wires powering your thermostat include: R-wire – Power, usually red. G-wire – Fan, usually green. Y-wire – Cooling, usually yellow.

What wire runs fan on furnace?

The red wire should be connected to the R terminal or the RH or RC terminal when the home has heating and cooling systems. The white wire connects to the W terminal, the yellow wire connects to the Y terminal and the common wire is used with digital thermostats and is usually black or blue.

How does a furnace fan limit switch work?

To put it very simply, the furnace fan limit switch is a control that tells your furnace’s fan when to turn on and off. So, when the furnace isn’t on, it tells the blower not to operate (and send cold air into your home) and when the furnace is on, it tells the blower to turn on and start circulating the warm air.

Can you run a furnace without a limit switch?

Without a functioning furnace limit switch, a furnace would not be able to regulate the temperature in conjunction with a thermostat. Typically, a furnace limit switch consists of an exterior plate and a temperature probe that lives inside the furnace housing.

How do you wire a furnace fan limit switch?

Quote from the video:
Quote from Youtube video: When temperature comes up then that would close and if it continues to go. Higher. Then this normally closed switch for the limit.

How do you wire a furnace fan switch?

Quote from the video:
Quote from Youtube video: Red wire goes where the our screw is the green wire goes where the G.

How do I connect my furnace fan to the thermostat?

Locate the “G” terminal, which controls the blower operation from the thermostat, on the board. Connect the green low voltage wire to the “G” terminal and put the access panel back on the front of the furnace. If no green wire exists you may need to pull a new thermostat wire from the furnace to the thermostat.

What kind of switch is the fan switch?

A single wall switch controls the power to the fan and light together, whereas a dual wall switch has two separate switches – one for the fan and the other for the light.

How do you test a fan limit switch?

Quote from the video:
Quote from Youtube video: To test the component. You can disconnect the wires. And check the resistance value across the contacts to see if it's open right now this switch is closed. And we read 0.0 ohms of resistance.

At what temperature does the fan limit normally closed?


The standard settings for most furnace fan limit switches are 200°F to shut off the burner, 130°F to turn off the blower, and 100°F to turn the blower back on.

How can you tell if a limit switch is bad?

Quote from the video:
Quote from Youtube video: Across the limit if it's not tripped. Which should be reading zero terrific Chris. Now he reads 24 volts that means that's a bad limit.