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How To Deal With An Inaccurate HVAC Thermostat

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Ever notice that your air conditioner's thermostat says one thing, but you feel something completely different? It's not out of the ordinary for a thermostat to give readings that are completely off the mark when it comes to your home's actual temperature. There are many reasons why this problem happens and the following shows how you can troubleshoot and fix your thermostat.

Underlying Causes

As mentioned before, there are several reasons why your thermostat may start reading your home's indoor temperatures inaccurately:

  • Having your thermostat installed in an inappropriate location (such as an exterior wall or in the direct path of a window) could cause it to read inaccurately over time.
  • The air inlet openings on the thermostat become blocked with dirt and debris over time, reducing airflow to the thermostat and subsequently making it harder for the unit to read accurate temperatures.
  • Older thermostats that rely on mercury switches may give inaccurate readings if the unit is accidentally knocked askew. The unit has to be level to read accurate temperatures.
  • Corrosion of the contacts inside of a thermostat can also cause inaccurate readings.

Keep in mind that excess humidity can also be a cause of seemingly inaccurate thermostat temperatures. Your skin releases heat through perspiration cooling. As you sweat, the evaporative effect removes heat and makes your skin feel cooler. As the relative humidity in your home rises, it becomes harder for this effect to work. As a result, a humid room often feels warmer than its actual temperature.

Testing Your Thermostat

If you want to know what the deal is with your thermostat, you'll want to put it to the test. For this, you'll need only a small digital thermometer along with a paper towel sheet and a few pieces of tape. Start by taping the paper towel sheet to the wall right next to the thermostat. The paper towel will provide something of a buffer zone so that the digital thermometer doesn't read the wall temperature instead of the air temperature you'll need.

Next, tape your thermometer directly onto the paper towel sheet and leave it in place for about 15 minutes. Afterwards, compare what you see on the thermometer with the temperature reading on the thermostat. If both readings are the same and you're still feeling hotter than the actual readings show, then you'll need to take steps to tackle your home's excess humidity. Otherwise, you should use the tips found below to correct your thermostat issue.

Fixing Your Thermostat

There are several steps you can take to correct your thermostat's inaccurate temperature readings:

  • Check if your thermostat is exposed to direct sunlight, an HVAC supply or return air vent or other external sources of heat or cold. If so, you'll want to relocate your thermostat, preferably to an interior wall close to the center of your home.
  • If your thermostat was knocked off-kilter, use a bubble level to straighten it out. Keep in mind that only older mercury thermostats are affected by this issue -- a digital thermostat's temperature readings won't be affected if it's not level.
  • Use a soft brush or compressed air to remove dust, dirt and other debris from the thermostat.
  • Use a soft cloth and some electronic cleaner to remove residue and debris from the contacts. If necessary, you can use fine grit sandpaper to remove corrosion from the contacts.
  • Try replacing the battery inside the thermostat. A low battery charge could create inaccurate temperature readings, in some cases.

Afterwards, use the previously mentioned test to verify that your thermostat works properly. If you're still getting inaccurate temperatures, then you may want to consider replacing your thermostat with a newer unit.


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