Why Is My Digital Thermostat Blank?

Great, you just got home, and you walk over to lower the temp on your thermostat but find it's blank. Now, what do you do? Here are a few of the most common reasons your thermostat has no display:Why is my thermostat blank
  • Tripped circuit breaker
  • Safety float switch tripped
  • Batteries need to be replaced
  • Control fuse is blown
  • Thermostat is defective

1. Tripped circuit breaker

Your thermostat receives control voltage a transformer located in the air handler. If the breaker is tripped, there is No voltage; no voltage means no display.

Simply resetting the air handler breaker (or check the fuse) could resolve the issue. Some systems have a breaker at the air handler but also in the main panel as well. If the switch is reset but trips immediately again, call an HVAC professional.

2. Float switch tripped

The float switch is a safety switch designed to shut the AC down to prevent water damage if your drain is clogged. When the switch is activated it breaks the control circuit thus breaking power to your thermostat- the thermostat goes blank.

The float switch is located near the bottom of the air handler if the air handler is vertical. You can usually pull the switch out to check for water either visually or by sticking your finger in to feel for moisture.

If your air handler is horizontal, there may be two switches. One on the air handler and one in the secondary pan under the unit. The switch may look different by design but perform the same function.

If there is water under the unit in the secondary pan, remove the water. Remember the drain line has to be cleared in scenarios or the problem will reoccur.

Dead batteries cause blank thermostat3. Batteries are dead

Some digital thermostats require batteries for the display.

Depending on the model of the thermostat, you may need to remove the faceplate from the wall to access.

There might also be a little access panel. Refer to the owner's manual.

4. Control fuse is blown

This one we recommend calling an AC contractor for because of the hazard of making the repair. Most AC units have a small 3-5 amp control fuse in the air handler. This fuse is designed to blow if too much amperage is sensed in the control circuit.

Typically this fuse does not randomly blow. There is a problem. This fuse is a blade type fuse commonly used in cars of a glass style fuse. Sometimes the transformer itself has a manual mini circuit breaker built into the side of it.

This circuit breaker can also be reset if it is tripped. Again, due to the high voltage in the air handler, We recommend that you do not attempt this option unless you are confident in dealing with electricity. Call a professional.

5. The thermostat is defective

It is possible that the thermostat failed. This does happen. If you have control voltage (24 volts) at the thermostat between the "r" terminal (power) and the "c" terminal (common) the thermostat should have a display. If your thermostat requires batteries and they are fresh, that's about all you can do. The thermostat may be bad.

We hope this helps. Of course, there are other reasons the thermostat may go blank, but these are the most common. Don't hesitate to call we can assist.

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