When issues occur within an air conditioning system, a common cause is the thermostat. The thermostat controls the automated features of the air conditioning system. When a thermostat does not function properly, the air conditioning system may not heat or cool as desired or may not function at all. You can troubleshoot thermostat issues when experiencing a non-functioning or unresponsive thermostat or a thermostat without back light. These troubleshooting steps can pinpoint the error and help determine if the issue is repairable or if the thermostat needs replacing.

Thermostat Power

Step 1

Remove the thermostat cover to expose the base and wiring of the thermostat. The thermostat will be located on an interior wall of the home. Depending upon the style of thermostat, the cover may simply pull away from the wall or screws could attach the cover to the wall.

Step 2

Touch the end of the voltage meter's pen device to the main power wire of the thermostat. The thermostat will have several differently colored wires. The main power wires to test are red and black. Touch the voltage meter to the red wire and check the reading for power and then to the black wire and check the meter reading for power.

Step 3

Determine if power is detected in the thermostat. Some voltage meters will illuminate the end of the pen device when power is detected and other meters will beep when power is detected. Read the instructions of the voltage meter to determine the correct indication of power. If either of the red or black wires do not have power then the issue is not the thermostat and will require an electrician.

No Thermostat Backlight

Step 4

Remove the battery casing or door to access the batteries. Every thermostat with a digital display or light will have batteries. Most commonly, thermostats will use two AA batteries to power the back light. Most thermostats have a battery casing located on the top of the thermostat that opens by pressing a marked tab and then pushing the battering housing outward and away from the thermostat. All thermostats have a marking to show the location of the battery housing.

Step 5

Replace the batteries with new batteries. Follow the guide in the battery housing on the correct direction to insert the new batteries. Replace the battery housing back into the thermostat by sliding it back into place and pressing easily until you hear the housing click into place.

Step 6

Reattach the thermostat cover and determine if the back light functions properly. The thermostat cover may just click back into place or may require replacement of the screws to secure the cover.

Thermostat Not Responding

Step 7

Inspect the settings of the thermostat.

Step 8

Check to see if the thermostat is programmed. If the thermostat is programmed, it may disregard the manual temperature setting and follow the programmed settings. If the thermostat is not responding to a manual setting and there is a program running, stop the programed settings of the thermostat to utilize the manual settings.

Step 9

Recalibrate the thermostat if it is not programmed. Read the manufacturer's instructions for the specific thermostat to determine the correct steps to take for recalibration of the thermostat. Thermostats respond to temperatures so it is vital that they read and interpret temperatures accurately. Recalibrating the thermostat will reset and correct any variances between the actual temperature and the temperature readings of the thermostat.