The thermostat controls both the heating and cooling systems of homes with central heat and air conditioning, or just the furnace in homes without air. The thermostat detects the temperature of the room and compares it to the desired temperature setting. If the room is too warm or too cold, the thermostat requests heat or air depending on the season.
Set the thermostat at least 5 degrees higher or lower than your normal setting, depending on the season. Set it 5 degrees higher than normal during heating season, and 5 degrees lower during cooling season. Check that the appropriate device comes on.
Determine whether another problem might cause the device not to work properly. Check that the thermostat is correctly set to “Heat” or “Cool.” Check that the main circuit breaker for the furnace or air conditioner is in the “On” position.
Turn off the power for the furnace and air conditioning systems by switching the appropriate circuit breaker to the “Off” position.
Remove the cover to the thermostat. They typically come off with gentle prying by hand.
Check the wires, making sure each is attached firmly to its respective mounting screw. Reattach any loose wires and tighten loose mounting screws.
Flip the breakers back on and determine whether the device runs by repeating Step 1. If it does not, turn the furnace and air conditioner power back off again at the breaker panel.
Study the wires inside the thermostat. Choose the red and white wires if you are having problems with the furnace kicking on, or the red and green wires if you are having issues with the air conditioning system coming on.
Unscrew the two appropriate wires from their terminals. As you loosen the screws, grip the wires with your other hand so they don’t slip behind the wall.
Wrap the two wires together, and turn the breaker back on. If the blower comes on -- for furnaces or air conditioning systems -- the thermostat is bad.
Things You Will Need
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