Emerson Thermostat Wiring [Full Guide]

In this guide, we’ll take you step-by-step through Emerson thermostat wiring and diagrams, making it a breeze for you to upgrade your home’s heating and cooling system.

Whether you’re a DIY enthusiast or a curious homeowner, our goal here is to provide you with clear instructions, practical tips to successfully wire your Emerson thermostat. So, let’s dive right into this practical thermostat wiring guide! 

emerson thermostat on wall 1

Preparing your Emerson thermostat for wiring

 Before you start wiring your thermostat, let’s follow these steps to ensure we are doing the right thing:

Turn Off Power: Before you begin wiring, turn off the power to the HVAC system at the circuit breaker. This is for your safety and to prevent any electrical accidents.

Remove the old thermostat cover: Remove the old thermostat’s front cover from the wall base. On many models you will pull off easily, while others you may need a screwdriver to remove it.

Identify Existing Wires: If you’re replacing an old thermostat, identify the wires connected to it and label them according to their corresponding terminals.

See table 1 for the translation of wire color code from old thermostat to new Emerson.

Read also: Troubleshooting Emerson thermostat [Full guide]

Remove Old Thermostat: Unscrew and disconnect the old thermostat from the wall. Be careful not to let the wires fall back into the wall.

You may need to wrap them around a pencil something to avoid this

Mount the New Thermostat Base: Install the base plate of the Emerson thermostat onto the wall. You may need screws and a screwdriver. Use the built in level to level it up.

Connect the Wires: Please  see the wiring diagrams in fig 2-5  Connect each wire to its corresponding terminal as in the image below:

connect wires to corresponding terminals 1
fig 1.

To connect wires to your new thermostAt terminals are usually labeled with letters corresponding to the wire colors. 

Install Batteries: Install the 2 AA batteries that come with the thermostat. Insert them into the battery  compartment in the correct direction.

inserting battery in emerson thermostat

Attach the Thermostat: Align the thermostat unit with the base plate and snap it into place. Ensure it is firmly attached and level.

Read also: How to reset Emerson/White Rodgers thermostat

Old thermostat wiring to Emerson thermostat wiring color code

There is no wire color code standardization for thermostat  wiring. However thermostats are typically wired with a common wiring color  but it all depends on the installer, he/she can wire according to what they feel is right.

Let’s take a look at the most wiring colors used in thermostat wiring from old thermostat to new Emerson thermostat together with thermostat together with their function.

Old thermostat terminal lettersLabel the wires with the following lettersTypical wire color Function
C, X, B* CBlueCommon Wire
RH, R, R5, 5RHRed24V Power (Heating)
RCRCRed24V Power (Cooling)
W, W1, W/E,Aux/E, EW/EWhite (Generally not fixed)1st Stage Heat (for conventional system); 1stStage Auxiliary Heat (for heat pump system)
GGGreenFan Relay
Y2Y2Light blueReversing Valve (for heat pump systems)
LLNot fixedHeat Pump Diagnostic
O, B*, O/BO/BOrangeReversing Valve (for heat pump systems)
W2**W2Brown2nd Stage Heat (Conventional) 2nd StageAuxiliary Heat (Heat Pump)
Y, Y1YYellow1st Stage Compressor
BC or O/B (It depends)Blue or Orange( depends)depends

Please note: If there is  wire in the O terminal in the old thermostat then you’re going to label the B wire as C. In case you have no wire in the O terminal on the old thermostat, you are going to label B as O/B.

Read also: Carrier infinity thermostat wiring

5 emerson thermostat wiring diagrams (Practical examples for 1f78 model)

3-wire thermostat wiring diagram for Emerson

This is one of the basic emerson thermostat wiring. If you have a heat only system your thermostat will only need 3 wires.

One for the fan relay which controls circulation of air and one  for the R or rh( power from the transformer and the other one  W for the heating system.  

The 3- wire is typical if you only have a furnace without an air conditioner.

1f78 heat only
fig 2.

3-wire wiring for cool only System ( Air conditioner only)

If you have a first stage air conditioner only, your thermostat will typically be connected to 3 wires, G, Rc and Y.

The Rc is power for cooling from the transformer , the G is  for the fan relay( controls the blower fan and helps circulate the cooled air.) This is another basic  wiring for any thermostat

1f78 cool only wiring
fig 2.

4-wire thermostat wiring for heat and cool system

The heat and cool system with an air conditioner and furnacec  will have four wires connected.

G wire (fan relay)

Y wire( compressor relay)

W wire ( for the heating system and he 

R wire power from the transformer (put a jumper betwen Rc and Rh if you have only one R wire)

If your thermostat has only these four wire, you probably have a first stage air conditioner with a heating system

1f78 cool heat
fig 3.

Read also: White Rodgers thermostat wiring

5 wire emerson thermostat wiring diagram

A 5 wire Emerson thermostat wiring diagram is typically for a conventional heating and cooling system with a dual transfer,  one for heating and the other for cooling. 

If you have a conventional air conditioner and conventional heating system such as a furnace, your thermostat will most likely use 5 wires.

1f78 Heat cool 5 wire dual transformer
fig 4. 5-wire wiring diagram

1f78 wiring diagram for heat pump ( energized in cool)

Wiring diagram for heat pump for Emerson 1f78 model

A heat pump system will also have a reversing valve.  The wiring for this type of system is interesting because you are not going to have a separate wire for the W terminal.

 Instead you will jump the Y and the W terminal. 

Then Rc and R will also be attached if there is only one R wire coming from the wall. 

In summary terminal that you should connected are:

Y terminal ( jumper it to W terminal

O/B

 Rc and Rh ( jumper)

G terminal and the

1f78 wiring diagram fr heat pump 1
fig 5.

FAQ

When should you jumper the wires?

It is important to know when to jumper the wires between Rc and Rch when you are wiring your Emerson thermostat.

Here are some of the important things to take note of:

  • When you have Terminal RC and RH connected with a jumper wire on your old thermostat then you should have a jumper on RC/RH on your new thermostat.
  • On your old thermostat, if you have only one R wire for all ( Rc, Rch or R5) coming out of the wall. Then you definitely need to place a jumper between Rc/Rh.
  • If on the older thermostat there are two separate wires coming out of the wall and are not jumpered together, then don’t jump the Rc and Rh on the new thermostat.

Final thoughts

That’s all you need to know about Emerson thermostat wiring. If you need more information or help for your specific model, you might want to go through the user manual. 

Otherwise if you are not comfortable dealing with the thermostat wiring yourself, I recommend that you seek help from a local qualified HVAC profession.

Thanks for reading.

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