Fixing a Malfunctioning Central Air Conditioner Thermostat

The reason most of us want a central air conditioner is to have a nice cool home without a lot of fuss or bother.  The most common reason for a breakdown is forgetting that as easy as a central air conditioning unit can be to use, there is some routine care it needs to continue functioning at its best.  

Preventive Maintenance is Key

Start early when checking out how well your central air conditioner has survived the winter.  Try it on the first day that winter seems to be slacking off so that if worse comes to worse and you need to call in a professional, it won’t be on a day when you are counting the minutes and beads of sweat as you wait for them to show up.  

What You Will Need for Maintenance and Repair:

  • A screw driver
  • A replacement fuse for the breaker box  

If the air conditioner will not turn on automatically follow these steps:

Step 1 – Check Breaker Switches

Check the main electrical panel for a tripped breaker or blown fuse. If there is other secondary circuit panels in home check these as well.  Reset the breaker or if a fuse is found to be blown then replace it.

Step 2 – Check the Power

Check the furnace power switch.  It should be turned on and the outdoor condenser’s power switch should also be on.  This switch is usually mounted on the outdoor unit.  In the same area there should be a metal box also mounted on the house wall which houses the 240 volt disconnect switch.  All of these switches should be in the on position.  

Step 3 – Test the Thermostat

Try turning off the power to the air conditioner and check the thermostat by removing the thermostat’s cover using the screwdriver.  Unscrew the wire from the Y terminal.  Then turn the power back on.  Carefully hold the wire by the insulation only and touch the exposed end to the R terminal.  Hold the wire there for about two minutes to see if the compressor will not kick on.  If it does than the thermostat is faulty and needs to be replaced.  Put everything back together before calling in a professional.

If the room temperatures running from too hot to too cold it might be a problem with the thermostat heat anticipator.

Step 1 – Check Thermostat for Level

Take off the thermostat’s cover (and if this is a mechanical thermostat with a mercury switch), use a level to see if the thermostat’s mounting is flush and level to the wall. If it isn’t, then this will keep it from taking proper temperature measurements.

Step 2 – Adjust the Thermostat

On other types of thermostats, you will see a level which moves along a scale than this is the heat anticipator for this thermostat.  If the thermostat is going on and off too frequently with this type of anticipator try moving the lever one mark away from its normal position.  It might take a few hours for the thermostat to stabilize after being reset so wait a before trying again.  Do this until you have achieved the desired temperature.

If you can’t get the thermostats to work as needed, consider replacing them.