Keeping My Power Bills Down

Think You Need a New Thermostat? Here's How You Can Make Sure

If the furnace and air conditioner act as the heart of your HVAC system, then consider the thermostat as the brain behind the operation. A thermostat failure can be a bit surprising, since it's the last part of your HVAC system you'd ever expect to suddenly stop working. If you think your HVAC system needs a new thermostat, here are some troubleshooting steps you can use to diagnose your thermostat.

Keep in mind that there are two common problems that prompt homeowners to have their thermostats replaced:

  • The thermostat's digital display is blank.
  • The display works fine, but the HVAC system won't respond to thermostat inputs.

If the Digital Display Is Blank...

Make sure the HVAC system hasn't tripped its circuit breaker or blown a fuse. If it did, reset the breaker or replace the fuse and turn the unit back on. If the breaker trips or the fuse blows again, then you might want to have your HVAC contractor take a look at the problem.

If the breakers or fuses haven't been tripped, flip the breaker in the "off" position or remove the fuse to temporarily shut off power to the HVAC unit. Next, carefully dismount the thermostat from its wall bracket and turn it over to locate the battery slot. Replace the batteries inside with a fresh set of AA-size, AAA-size or CR2012-type batteries. Afterward, remount the thermostat and restore power to the HVAC system.

If the display is still blank, you'll want to try the following:

  • Make sure the battery is oriented in the correct direction, with the positive side facing the positive terminal and the negative side facing the negative terminal.
  • Check the battery terminals and thermostat wiring for signs of corrosion. Use a piece of fine sandpaper or electronic cleaner to remove the corrosion.
  • Use compressed air to blow dust and debris out of the thermostat.

If none of these steps seem to fix your thermostat woes, then it's time to replace your thermostat with a newer one.

If the Thermostat Is Unresponsive...

Set the thermostat to "cool" to trigger the air conditioner or to "heat" to trigger the furnace. Make sure the blower fan setting is on "auto" instead of "on." If possible, have a partner stand next to the indoor HVAC system cabinet so he or she can listen to the unit as it turns on. Next, trigger the furnace or A/C by adjusting the desired thermostat temperature five degrees higher or lower than the current room temperature. At this point, you should hear the relay within the thermostat click once as it sends the signal for heat or air conditioning to the HVAC system. The furnace or air conditioner may also click

If the thermostat clicks but neither the furnace nor air conditioner comes on within five minutes, you may need to check the thermostat wiring before replacing the entire unit. Make sure all of the wires are making proper contact with the wiring terminals. If necessary, trim off any excess insulation before inserting the wire into its proper terminal.

If the HVAC unit is still unresponsive, remove the red and white wires from their respective terminals and twist the two together to trigger the heating system. If the heating system starts operating, then the problem is with the thermostat. If the heating system remains dormant, then the problem lies somewhere within the HVAC system itself.

If the thermostat remains silent regardless of any input, then it's likely that the thermostat itself has failed. At this point, you should replace the thermostat with a similar model or take the opportunity to upgrade to a programmable or Wi-Fi smart thermostat, if you haven't already.

Talk to a company such as Weather Control Air Conditioning, Inc. for more information about AC repair.