/ / Dometic 3-Wire Thermostat Wiring Diagram: How To Connect Safely

Dometic 3-Wire Thermostat Wiring Diagram: How To Connect Safely

Thermostats manage most heating, ventilation, and air conditioning (HVAC) systems. Knowing about the Dometic 3-wire thermostat wiring diagram might come in handy if you ever need to replace an old one or figure out what’s wrong with a brand-new one.

In this article, we have provided a detailed guide regarding which color wire goes where, some common failures with their solutions, and lastly, we will discuss 2-,3-,4-, and 5-wire thermostat installations comprehensively.

Let’s dive into the detailed guide!

Common Failures with Dometic 3 Wire Thermostat

Many recreational vehicles and mobile homes use the Dometic three wires thermostat to regulate the temperature inside. Although these thermostats are usually dependable, they are prone to a few typical malfunctions.

Dometic 3-wire thermostat wiring diagram
Source: https://www.arprv.com/

Several potential failures, along with their solutions, are listed below:

1. Irresponsive Thermostat

If the thermostat is unresponsive, it may be time to change the batteries. If the thermostat is hardwired into the building’s electrical system, check the circuit breaker to make sure it is receiving electricity.

2. Difficult to Turn on Furnace or AC

Check the HVAC system’s power source if the thermostat is properly adjusted, but the heater or air conditioner still won’t turn on. Verify that the Dometic thermostat is at the proper setting (heating or cooling).

3. Inaccurate Temperature and Heat Pump Readings

If the thermostat is giving you false readings, try moving it to a different location. The thermostat needs to be kept in a cool, dark place out of the path of any potential heat sources, including direct sunlight. Make sure the thermostat isn’t crooked, either.

4. Unable to Turn on Fan

The thermostat setting for the fan’s speed may need to be adjusted if it won’t turn on. Both “Auto” and “On” are available for controlling the fan’s operation. When the thermostat detects that the heating or cooling system is on, the fan will only activate in the “Auto” setting. When the switch is “On,” the fan operates nonstop.

5. Faulty Thermostat Display

If the thermostat’s screen is malfunctioning or displays inaccurate information, you may reset it by unplugging it from the wall and leaving the wires disconnected for a few minutes before reconnecting them.

6. Wiring Problem

Make sure the thermostat’s wires are securely connected. Thermostat issues might be caused by sloppy electrical connections.

Note: If none of those work, you might want to think about getting a new thermostat. Always check the manual before using it.

Accessing the Colored Wires by Removing the Control Box of Dometic Thermostat

When starting with wiring a Dometic thermostat, the first step is to access the wires. Typically, the thermostat is mounted on the wall, and removing the control panel will reveal the wiring. It is important to ensure that the thermostat is disconnected from the electricity before proceeding.

  1. To detach the panel, you may need to gently push it downward or upward.
  2. Access to the wiring terminals can be obtained by removing the screws on the thermostat.
  3. Once you remove the control panel, you will find the base and protruding cables located beneath it.

Note: A basic thermostat typically includes left and right-side plugs for eight wires each. Before removing the panel with a flathead screwdriver, it is essential to understand the significance of wire colors and codes in the thermostat’s wiring.

The connections on the thermostat are as follows:

Dometic Thermostat Wiring Color Codes

Symbols such as Y2, 2x ODT, AUX NO, O/B, C, R, W1, W2, G, Y1, AUX CBK, 2x RS, and AUX NC, are commonly found on the thermostat base, which usually has 16 available plugs. However, not all of these features are available on 2, 3, or 4-wire thermostats. Additionally, some plugs may not have wires installed, which is also common.

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Each thermostat terminal is identified by a specific wire color:

Black/Blue Thermostat Wires (“C” Wire)

Usually, the “Common” or “C” wire is identifiable by its black or blue color:

  • Its purpose is to complete the 24V electric circuit by connecting the transformer to the C wire.
  • In modern thermostats, there is a constantly looped 24V circuit, whereas older versions only completed the loop when the power was needed, such as when turning on the AC.
  • Dometic’s digital thermostat still uses power even when the HVAC system is turned off.

Red Thermostat Wire in Dometic (“RC” or “R” Wire)

The “R” wire, also referred to as the red wire:

  • It serves as the power wire and is in charge of delivering 24-volt AC electricity to the thermostat
  • The electricity is sourced from the transformer found in the air conditioner‘s air handler.
  • The red wires are present in every AC units and are responsible for supplying power to the thermostat.
  • For dual transformer systems, there may be either RC or RH connections, which require slightly different wiring procedures.

White Thermostat Wire in Dometic (“W1” or “W2”)

The white wire is commonly associated with heating systems and is typically found in Dometic thermostats used for gas furnaces, but they are not commonly found in AC thermostats.

  • The W wires establish a direct connection between the thermostat and the heat source, which may be a furnace or a heat pump.
  • In the case of two-stage heating zones, the W2 wire is necessary for the second stage of heating found in most heat pumps. The white W2 wire is typically used for this purpose.

Dark Blue WiresFor B And Orange Wire For O (“B/O” Wire)

In a thermostat system, the orange wires have the task of managing the reverse valve, which functions in the reverse direction of the forward flow.

  • This wire connects to the condenser and is commonly found in heat pumps from major brands such as Trane, Goodman, Lennox, and others.
  • It is placed in the heat pump outdoor unit.
  • In some systems, the reversing valve in heat pumps is activated when the heating mode is engaged, and the t-stat terminal requires a dark blue “B” wire for this purpose.

Green Thermostat Wire in Dometic (“G” Wire)

The green wire, also known as the “G” wire:

  • It is responsible for connecting the fan to the indoor air handler in a mini-split system.
  • This wire controls the amount of electricity sent to the fan and is typically connected to the fan relay to turn it on and off as needed.

Y1/Y2 or Thermostat Yellow Wire in Dometic

The Y terminals serve as the connection points for the compressor relay:

  • Are typically wired to the air handler of an indoor split-system unit.
  • In most American homes, one-stage cooling or Y1 is the standard, and the Y wire coded as “Y1” is usually colored yellow.
  • If you are unable to figure out the wire size for your air conditioner, you can get some ideas from here.

The “Y2” terminal is specifically designed for air conditioners that have second-stage cooling capability. This terminal is only required if you have:

  • Two compressor
  • 2-stage compressor

Other Wires

These connections ODT1, ODT2, AUX NO, AUX NC, BK, RS1, RS2, and AUX C, are located on the right side of the thermostat and are rarely used.

Removing The Old Thermostat

Before discarding the old thermostat, it is important to ensure that the new thermostat can be successfully wired. You must have become knowledgeable about the color-coding system and can replace a basic thermostat without requiring any rewiring.

If you intend to wire the thermostat on your own, the simplest measure you can take is to do the following prior to putting an end to the old thermostat.

Capture and Save a Picture

If you disconnect the terminals too quickly by unscrewing them, it may become challenging to reconnect the wires to the new terminal. Therefore, it is recommended to take a photo of the old thermostat’s wire setup before proceeding to remove it.

Having a photo of the old Dometic thermostat setup will be a helpful reference to make sure that the wires are connected to the appropriate terminals on the new thermostat.

Make Sure to Spead the Wires

After capturing a photo of the old Dometic thermostat, it can be discarded. However, it is important to proceed with caution as the thermostat serves as a support for the wires, keeping them away from the wall. If the thermostat is removed immediately, the wires may become tangled or caught in the wall.

To prevent this:


  • Create a hole in the wall measuring around 2×2 inches
  • Ensure that the wires have a diameter of approximately 1×1 inch
  • By separating the wires, you can make a cross-section of at least 2×2 inches, allowing the wires to be supported on the wall.

If you follow this procedure, you can safely remove the old thermostat without causing any damage to the wires or the wall.

Installing A New Dometic Thermostat Control Board by Reconnecting Wires

When you change a Dometic thermostat, it is important to install the new one in the same spot as the old one and pass the wires from the wall through the opening of the new thermostat.

When reconnecting the wires, it is helpful to have a picture of the current thermostat for comparison. Two methods exist for determining the proper connection of each wire:

  • Referring to the photo and reconnecting the wires according to their previous setup
  • Using color codes to reconnect wires correctly

If you opt to use color codes, you may refer to the section mentioned earlier to identify the purpose of each wire. Here’s a summary for your convenience:

  • 24V Power (Red Wires)
  • Fan (Green Wires)
  • Cooling (Blue Wire)
  • Heating (White Wire)
  • Cooling power (Rc)
  • Heating power (Rh)

Protecting the wire by securing it onto the appropriate terminal and tightening it in place is all that’s required. To ensure that the wire is firmly attached, you can give it a gentle tug. After you’ve finished reconnecting the wires, reinstall the control boards and verify that it’s functioning correctly.

Dometic Thermostat Wiring for Furnace (2 Wire)

The simplest type of thermostat employs only two wires, typically colored red and white, and doesn’t necessitate a “C” or “Common” wire when linking to a furnace.

This makes installation quick and easy, using the following standard color scheme for connecting a two-wire thermostat:

  • Red wires: for power (24h).
  • White wire: for heating.

DIY instructions to replace a two-wire thermostat:


  • Dismantling: To start, disassemble the control panel of the old thermostat.
  • Take Notes: Make sure that the red wires linked to R are firmly connected, while the white wires are connected to Rh or W1. It is also advisable to take a photo of the connections for future reference.
  • Unscrewing: Unscrew the two wires from their terminals.
  • Motherboard Replacement: Replace the old unit with the new motherboard if necessary.
  • Reconnecting: Reinstall the control panel by reattaching the white and red wire and tightening the set screw.
  • Testing: Turn on the heat source to test the wiring of the new two-wire thermostat.

Dometic 3-wire Thermostat Wiring Diagram for Boilers and Heaters

Most modern boilers and water heaters are operated by three-wire thermostats, which are identified by the colors G, W, and R.

The “G” or green wire is a notable aspect that distinguishes between two-wire and three-wire thermostats, and it is often utilized for regulating fans. In a three-wire thermostat, the green wire serves as the shared connection that is used repeatedly.

Source: https://www.softstartrv.com/

The correct color sequence for connecting the only three wires of a thermostat is shown below:

  • 24V power (red wire)
  • Heating (white wire)
  • Recovered C wire (green wire)

For wiring a three-wires thermostat, follow these steps:

  • Removing Control Panel: Eliminate the previous thermostat’s control panel, and capture an image of the three wires. Take note of the colors (red, white, and green) and the terminals to which they are connected (marked R, W, or W1).
  • Disassembling: Disassemble the previous thermostat until you locate the motherboard, and then secure the connections with tape to prevent them from slipping behind or above the wall.
  • Motherboard Replacement: Replace the motherboard and feed the wires through the openings of the three-wire thermostat.
  • Screw Tightening: Ensure that the terminal screws are tightened and that the wires are connected correctly (green to G, white to W/W1, and red to R).
  • Installing: Install the control panel and verify that it is functioning properly if your boiler or water heater uses a three-wire thermostat.

4-Wire Dometic Thermostat Wiring for Heat Pumps and AC Unit

Thermostats with 4 wires offer more flexibility for customization. Smart thermostats such as Dometic require a 4-wire connection for optimal performance.

Source: https://www.softstartrv.com/

In addition to the heating wire, which is present in 2-wire thermostats, and the C or fan wire, which is present in three-wire thermostats, cooling wire is also present in 4-wire thermostats, typically colored blue or yellow.

The following figures show the terminal designations and corresponding wire colors used in a four-wire thermostat.

  • 24V power (red wire)
  • Heating often connected to W/W1 (white wire)
  • Fans (green wire)
  • Cooling (blue/yellow wire)

Heat pumps, which can provide both cooling and heating, typically use thermostats with four wires. The green wires are required to operate the fan and generate airflow.

Here are the instructions for installing a 4-wire thermostat:

  • Remove Panel: To get to the wiring in your 4-wire thermostat, you’ll need to remove the panel.
  • Take a Picture: Taking a picture of the cables is much easier than trying to remember where each one wire goes.
  • Motherboard Removal: Remove the motherboard and tape down the cables; the four of them will disappear into the wall if you don’t.
  • Motherboard Replacement: You may now replace the motherboard by screwing it in and threading the four cables through the opening.
  • Re-Screwing: Securely reconnect the 4 wires to their respective terminals using the e-screws, with the red wire to the R terminal, white wire to the W or W1 terminal, green wire to the G terminal, and blue or yellow wire to the Y terminal. Ensure that each wire is firmly attached by pulling on it.
  • Testing: Start the heat pump or any air conditioning and heating unit that communicates with a 4-wire thermostat.

5-Wire Dometic Thermostat Wiring for All Appliances

A 5-wire thermostat can be considered a 4-wire thermostat with an additional “Common” or “C” wire. In HVAC systems, several digital thermostats require a 24V C wire connection to function correctly.

5-wire thermostats are highly versatile and can be used to control a variety of modern HVAC systems, including smart air conditioners, heat pumps, and furnaces. The followings are the terminal codes and wire colors commonly used for a 5-wire thermostat.

  • 24V Power (red wire)
  • Heating (white wire) and is connected to the W/W1
  • Fans (green wire)
  • Cooling (yellow/blue wire) often connected to the Y terminal.
  • “C” or “Common” (black wire)

Below is a set of instructions on how to install a new thermostat to replace an existing 5-wire thermostat.

  • Panel Removal: In order to access the wiring of your 5-wire thermostat, you will need to remove the panel.
  • Take a Photo: It is much more convenient to take a photo of the cables than to try to remember their placement.
  • Remove the Motherboard: Make sure to remove the motherboard and secure the four cables with tape, otherwise, they may disappear into the wall.
  • Attach a New Motherboard: Once the new motherboard is attached with screws, feed the five cables through the opening.
  • Screw Wires: Verify that the red wire is securely connected to R, the white wire is properly attached to W/W1, the green wire is firmly connected to G, the blue or yellow wire is securely connected to Y, and the black wire is properly connected to C. Double-check that each wire is firmly connected by lightly pulling on them.
  • Checking: Test the connectivity of the 5-wire thermostat by powering on any connected smart devices and attempting to operate them through the app or remote control.


Should I Replace the Dometic 3 wire with Coleman 4?

Replacing depends on you! It’s common for replacement thermostats to have universal compatibility. However, it might be difficult to switch to Coleman 4 thermostat if you have a unique Dometic 3 system.

How do you reset a 3-button Dometic thermostat?

To reset 3 buttons Dometic single-zone thermostat, start by turning it off. Next, press and hold the On/Off Mode button for three seconds, while also pressing the + button at the same time. These steps should help you successfully reset your thermostat.

Which wire is hot on a 3-wire?

The hot wire on a 3-wire is black in color and is commonly referred to as the “line wire” or “common wire”. It connects the power supply to the first switch in a 3-way configuration. It remains constantly live, except when the circuit breaker is turned off.

What happens if you connect the thermostat wires wrong?

If you connect the thermostat wires wrong, the entire system becomes inoperable, leading to potential issues such as high energy bills, an uncomfortable environment, or system failure.

What are the three wires on a thermostat?

The three wires on a thermostat include a white cable indicating that the thermostat is used to regulate the heating system. The yellow (Y) cable connects to the compressor of your air conditioner, while the green G wire powers the ventilation fan.


The Dometic 3 wiring diagram is a crucial guide for installing and setting up a Dometic RV thermostat. It is important to follow the diagram carefully and ensure that all connections are made correctly to avoid any electrical issues or malfunctions.

Have you ever faced any wiring issues while on a road trip? Which thermostat wiring diagram is the best fit for your RV? Let us know your answers in the comment section below and feel free to provide your feedback regarding any queries!

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