Lux DHP2120 Installation Manual

Lux DHP2120 Installation Manual

Thank you for your confidence in our product. You should become fully acquainted with this thermostat before installing it for usage. Follow the installation procedures carefully, and one step at a time. This will save you time and minimize the chance of damaging either the thermostat or the systems that it controls. These instructions may contain information beyond that required for your particular
installation.  Please save these instructions for future reference.


  • The DHP2120 thermostat can be used with most 24 volt: single- stage heat pumps, and 2 heat / 1 cool heat pump systems.
  • This thermostat cannot be used to control: conventional heating and cooling systems, 3-wire zone valves, or 120/240 volt (line voltage) heating or cooling systems. Ask your dealer for other LUX® thermostats to control those systems.

Lux DHP2120 Thermostat Location

On replacement installations, mount the new thermostat in place of the old one unless the conditions listed below suggest otherwise. On new installations, follow the guidelines listed below.

  1. Locate the thermostat on an inside wall, at about 5 ft. (1.5m) above the floor, and in a room that is used often.
  2. Do not install it where there are unusual heating conditions, such as: direct sunlight, near a lamp, television, radiator, register, fireplace, on a wall opposite a stove, or that carries hot water pipes.
  3. Do not locate in unusual cooling conditions, such as: on a wall separating an unheated room, or in a draft from a stairwell, door, or window.
  4. Do not locate where air circulation is poor, such as: in a corner or alcove, or behind an open door.
  5. Do not locate in a damp area. This can lead to corrosion that may shorten thermostat life.
  6. Do not install the unit until all construction work and painting has been completed.

Setup Option
If batteries are presently installed, remove them from the thermostat before proceeding with changing any of the options listed below. A table similar to this one shown here is printed on the thermostat's
circuit board.


There are 2 option jumpers located inside the thermostat on the circuit board. These settings can be changed from their default values by removing its corresponding black shorting cap and installing the cap so that it is positioned on the adjacent pair of metal pins. A change to either of the option jumpers will not be recognized unless the thermostat has been without battery power for at least 2 minutes, and then power is restored again. Each of these jumpers changes  a  different setup  option. The choices for these options are listed in a table printed on the circuit board, and are also printed adjacent to each individual setting jumper.


This setting controls whether the temperature is shown in degrees °F or °C on the LCD display screen.


This setting determines how the thermostat will use the shared B/O terminal connection on the back plate. Select the “B” option to have the B/O terminal powered while in heat mode, and un- powered while in cool and off modes. Select the “O” position to have the B/O terminal powered while in cool mode, and un-powered while in heat and off modes. If you are not sure which way to set this option, consult the manufacturer of your heat pump unit.

Once all optional jumper settings have been performed as described in the previous section, ensure that the thermostat has been without battery power for at least 2 minutes for the change to be recognized. Now install new batteries into the thermostat.  When installing batteries, use two new Energizer® or DURACELL® “AA” size alkaline batteries only. Ensure that the batteries are installed in the proper direction as per the markings shown in the battery tray.



While in HEAT, COOL, or EMER modes, a single press on either the UP or DOWN button causes the word “SET” to appear on the screen, and the set temperature value on the screen to start flashing. When flashing, the set temperature can be altered by pressing either the UP or DOWN button once per degree of change, or by holding either button for at least two seconds to automatically increment the set temperature quickly in the associated direction.

Based upon  the relationship of  the set temperature  to the displayed ambient room temperature, the thermostat will engage the first stage of either heating or cooling, if a temperature demand is present. If there is a large thermal demand present which is greater than the first stage of heating can accommodate, then a second stage of heating (W2) will be activated, showing the word “AUX” on the display screen. There is approximately a 4-minute delay that is imposed between the activation of the first stage of heating, and the second stage of heating.


Pressing either set temperature button will illuminate the display. The light will remain on for approximately 12 seconds. While the light is illuminated, pressing any of the 2 push buttons will cause the light to remain on for approximately 12 more seconds.


This is determined by the thermostat, and controls the minimum length of time that the thermostat must remain with Heat or Cool either On or Off, before it will automatically switch to the alternate On or Off state. This feature prevents rapid or short cycling, and also provides compressor protection. The duration of this delay is fixed at 5 minutes between on or off load changes.


There are two independent set temperature stops: a maximum heat set temperature, and a minimum cool set temperature. Each of these temperature stops is user adjustable in one-degree increments. The heat temperature stop prevents the set temperature from being adjusted higher than the heat temperature stop value. The cool temperature stop prevents the set temperature from being adjusted lower than the cool temperature stop value. To set the heat and cool temperature stops, place the system mode switch in the OFF position. Press and hold the UP key while sliding the mode switch from either OFF to HEAT (to adjust the maximum heat set temperature), or from OFF to COOL (to adjust the minimum cool set temperature). “Ht Lim” or “Cl Lim” will be displayed on the LCD screen while you are setting the heat or cool limits respectively. While in the adjustment mode for each of the temperature stops, use the UP and DOWN buttons to adjust the limit value, just as you would for adjusting the set temperature under normal operation.

NOTE: If no buttons are pressed for 4 seconds, the thermostat will accept the limit value that was on the screen, and return to normal operating mode, for the current mode switch position. Once,
complete, you should return to the adjustment mode again for both heat and cool to confirm your desired settings for both temperature modes have been accepted.


  1. The DASHED lines in wiring diagram #1 are optional depending upon your system type. Single stage heat pumps will not have wires present for the “E” or “W2” terminals. For a 2-Heat / 1-Cool system with NO Emergency heat wire, AUX heat will be connected to “W2”. A jumper wire may be placed in between the “E” and “W2” terminals to allow Emergency Heat Mode.
  2. For Heat Pumps, use either the “B” or “O” wire, NOT BOTH.
  3. If “Y” and “C” wires are both present, then “C” is a common wire. Do not connect this “C” wire to your thermostat.
  4. If you have a “B” wire in your system that is used as a common wire, connecting it to the “B/O” terminal on this thermostat may damage your system and/or the thermostat.


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Title : Lux DHP2120 Installation Manual
Format : PDF
Pages : 2 Pages
Language : English
File Size : 1 MB

Lux DHP2120 Installation Manual 

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