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Air Conditioner Or Heater Not Powering On - Thermostat Issues

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It can sometimes be problematic to determine whether your HVAC system or the building circuitry is at fault when a unit fails to power up properly. One of the most common culprits is the thermostat, and not the heater or air conditioner. There are steps that can be taken to determine whether your heater or air conditioner is actually malfunctioning, or if it is your thermostat. In fact, it is highly likely that the thermostat or the building power has an issue if both the heater and air conditioner will not kick-on. Read this article to learn more. 

Troubleshooting a Thermostat

There are many reasons why a thermostat might not work properly. The circuit breaker might have shut down, the batteries might have died, or the unit might be clogged with dust and debris on the inside. Many issues are obvious, and can be solved with a common sense approach. A dirty thermostat can often be repaired simply by cleaning it, for instance.

If the issue is not obvious from the outside, and you believe the thermostat is at fault, perform two simple actions first. Take out and replace the batteries if the unit has them. If the unit runs off of a circuit breaker, turn the breaker off and wait a moment, then turn it back on. If tripping the power to the thermostat does not fix the problem, you will need to delve inside it.

Make sure the power is off to the thermostat. Open up the front cover and take a look. If you see loose or corroded wires, or an inordinate amount of dust or other things inside the unit, then you may have found the problem. 

The thermostat for HVAC unit can usually be checked easily by accessing the wiring. You will need to remove the cover of the thermostat, then look for a row of wires and screws labeled with terms such as R and Y. In combined units where the thermostat controls both the heat and the air conditioner, the R wires may be labeled Rc and Rh. You can consider this to stand for R-cooling, and R-heating.

In many instances these wires will also be color coded. The HVAC wire colors you may wish to look for are red, green, and white. The red wire is usually the Y wire. The white wire is normally the furnace wire. The green wire is normally the air conditioner wire.

Once you have found that row of screws, you may undergo a step-by-step process to determine whether your thermostat or your heater or air conditioner is at fault.

  1. Make certain that the power to the air conditioning unit is off. Turn off the breaker if necessary. 
  2. Put on insulated gloves suitable for electrical work. 
  3. Unscrew the Y terminal wire and pull it away slightly. 
  4. Turn the power back on to the unit and then place the loose wire against the R terminal for a few minutes, usually two minutes will be long enough. Alternatively you can tie the Y wire to either the Rc or Rh wire, depending on whether you want to test your air conditioner or heater, and then turn the power on.  
  5. If the unit turns on, then your heater or air conditioner is fine. However, you have a faulty thermostat.

It is possible to replace a faulty thermostat yourself. However, if you feel uncomfortable with doing that sort of work on your own, call an air conditioning repairman. If your compressor or blower does not turn on no matter how long you hold the Y wire against the R terminal, and you are certain that the power is on, you will have to call an air conditioning and heating service because your furnace or air conditioner needs repair.