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» Support DMH110

Troubleshooting Poor Temperature Regulation
• This page lists problems that may affect the temperature performance of your LUX thermostat with suggested resolutions.
• For more detailed information please refer to the instructions that came with your thermostat.
The instruction manual for this model can be viewed in PDF format by clicking here.
 
Model DMH110
   
Problem Resolution
No fan function in heat mode Move the switch or jumper on the circuit board to its ELECTRIC position for electric heat.
Fan on continuously Move Fan switch from ON to Auto
  Remove the "G" wire. If fan continues to run, then either the system is mis-wired, or the problem is in the system, not the thermostat.
Indicates incorrect room temperature Refer to thermostat  manual to verify that your set temperature is what you expect it to be. The set temperature is always flashing when it is visible. "SET" is also visible then indicating that it is the set temperature.
Your thermostat offers a calibration feature. This feature may be used to adjust the displayed temperature up to +5F(3C) or -5F(3C) degrees.
What does the SAVE feature do The SAVE button allows you to use one button press to easily decrease the SET temperature in winter and increase the SET temperature during summer. Whenever you leave the house, touch the Save button to put it in Save mode. By default this will add 5 degrees to your set temperature in cooling and subtract 5 degrees from your set temperature in heating. When you return, touch the Save button again to cancel the “Save” mode and return your home to your previous SET temperature. 
Heats or cools more than 5 degrees past its displayed set temperature  Refer to thermostat manual to verify that your set temperature is what you expect it to be. The set temperature is always flashing when it is visible. "SET" is also visible then indicating that it is the set temperature.
  Remove thermostat body from the wall, leave the back plate in place. Verify that Heating and cooling switch off within a few minutes.
  If the thermostat is battery powered only, replace its batteries with fresh Duracell® or Energizer® alkaline batteries.
  Set unit to heat mode. Adjust set temperature to at least 5 degrees below room temperature. Then adjust set temperature upward one degree at a time. Listen carefully for a soft click from the thermostat. This click should be heard near room temperature.
   Refer to your unit's manual to decrease the units swing setting to a narrower setting.
  Verify that your unit's placement and mounting are optimum per the installation section of its manual. 
  Refer to wiring to verify that it is according to the wiring diagram for your system.
No heat or cooling when expected. Note that in Cool Mode the thermostat may not activate a cooling stage until its compressor protection time has elapsed this may be a long as 5 minutes.
  Refer to thermostat manual to verify that your temperature set point is what you expect it to be.
  Replace the batteries with fresh Duracell® or Energizer® alkaline batteries. Press reset with small Phillips screw driver. It may be necessary to reconfigure some settings after a reset.
  Set unit to heat mode. Adjust set temperature to at least 5 degrees below room temperature. Then adjust set temperature upward one degree at a time. Listen carefully for a soft click from the thermostat. This click should be heard near room temperature. Adjust set temperature down one degree at a time. Again listen carefully for a soft click from the thermostat near room temperature. 
  The brass contacts in your thermostat may need to be cleaned and/or tightened. Each contact is comprised of a pin protruding from the rear of the thermostats circuit board, and two V shaped two contacts on its wall plate. These contacts are located above each screw terminal.  Insert a small regular screw driver at one side of a "V" contact. Turn the screw driver to slightly bend the top of each "V" contact toward it's mate.
  Refer to wiring to verify that it is according to the wiring diagram applicable to your system.
Advanced Trouble Shooting If your system is a low voltage system having 24VAC or less, and you are technically inclined, you may jump terminals as given below out to detect a malfunction in your system. 
Fan Test FAN TEST: If your system has a fan, test it first.
  If the system is Heat only, or if there is a jumper between the "RH" and "RC" terminal of your thermostat, then with the power ON at the fuse box, touch the "G" wire to the "RH" terminal. The fan should come on immediately and stay on. The rush of air is usually easily heard.
  If the system is Cool only, or if the system is Heat and Cool and there are separate wires to "RH" and "RC",  and there is no jumper between them: then with the power ON at the fuse box, touch the "G" wire to the "RC" terminal. The fan should come on immediately and stay on.
  If the fan does not come on it is an indication that there is a problem with your system. Check any breaker o fuses that fed the 24VAC transformer that powers your system 
  If persists, contact qualified service personnel for aid in determining the fault.
Heat Test To test gas or oil heating systems, take the "W" wire off its terminal. With the power ON at the fuse box, touch the "W" wire to the "RH" terminal for a couple of minutes and the heater should come on and stay on until the wire is removed.
Cooling Test To test cooling, remove the "G" and "Y" wires. Connect them together with the "RC" for several minutes to observe operation. The system should come on and stay on. If the cooling fails to come on, or comes on and off, the problem is in the system.
Heat Pump Test To test a heat pump system with an "O" wire, three wires must be connected together with the power terminal. The power terminal is "RH" and "RC" with a jumper between them.  With the power ON at the fuse box, connect the "O"  and "Y" or  and "G" wires to the "RH" terminal for a couple of minutes and the unit should provide cool air. Wait at least 5 minutes and repeat this test without the "O" wire. The unit should provide Heat.  
  To test a heat pump system with a "B" wire, three wires must be connected together with the power terminal. The power terminal is "RH" and "RC" with a jumper between them . With the power ON at the fuse box, connect the "B"  and "Y" and "G" wires to the "RH" terminal for a couple of minutes and the unit should provide warm air.  Wait at least 5 minutes and repeat this test without the "B" wire. The unit should provide cool air.  
For further assistance: Contact your HVAC service company or our Technical Assistance Line if not resolved.
 
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