Troubleshooting AC Thermostat

Electronic thermostat displaying temperature and time with a blue lit background.
What You'll Need
Voltage meter
Cleaning brush
Bond paper

An AC thermostat that won't work can be incredibly annoying. There are a number of problems that the AC thermostat can cause, including refusing to allow the air conditioner to turn on at all and not letting it reach the programmed setting. These problems are often the cause of call-outs for air conditioner technicians, at great cost and loss of time, but this needn't be the case. If you have a few basic home improvement skills, and the manual of your AC thermostat to hand, then by following some very simply rules, you should be able to troubleshoot your air conditioning unit with no problems at all.

Step 1 - AC Doesn't Turn On

If your air conditioning unit won't come on at all, then you should check the thermostat. Turn off the power at the wall before doing any investigation. Firstly, ensure that there is power to the thermostat, both by checking the wiring supply to it, and also by replacing the batteries. Try turning the power on again. If nothing happens, turn power off and proceed. The next thing to do is to check that the thermostat is clean, and that it is not faulty. The latter can be done by turning the power on, setting the thermostat, and watching as it goes through the motions.

Step 2 - Temperature Exceeds or Doesn't Reach Programming

Another major problem with a faulty thermostat is the temperature control. If you are finding that the AC unit is making the room too cold, despite having programmed the thermostat to a suitable level, you need to check that the thermostat is working correctly. Firstly, use the Voltmeter to ensure that the right amount of voltage is reaching the thermostat. If not, then you can recalibrate it by removing the thermostat cover, locating the ampere, and setting it to the factory recommended setting, as described in the manual.

An AC unit will require the ampere setting found at the last stage of the manual's instructions. Another problem may be that the thermostat is not level, causing the temperature gauge inside to be misaligned. Use a level to check the alignment, and adjust it if it is out of sync.

Step 3 - Thermostat Needs a Clean

Dirt in the AC thermostat is one of the most common causes of problems, so a good troubleshooting method is to just clean the thermostat. First, ensure the power is turned off, and then remove the cover of your thermostat. Locate the bimetal coil inside, and brush it free of dust using a soft brush, such as a shoe polish brush. Unscrew the body of the thermostat, and brush off the top and the mounting plate. Use a piece of cleaning paper, known as bond paper, to remove any dirt between the contacts.

Check that there is no dust and debris on any other part of the thermostat, and then reinstall. Turn the power back on, and program your AC thermostat for your ordinary cooling requirements, then wait to see whether your troubleshooting has worked.