The thermostat is the central control of your HVAC system, and malfunctioning can prevent the AC and furnace from turning on. This problem can be due to bad wiring connecting the thermostat to the AC and heater, or a thermostat that has reached the end of its life.
When your thermostat is working correctly, you can keep it as cool or warm as you need. A bad thermostat can cause your AC to not cool or heat the room to the desired temperature. Air conditioning concerns are more apparent: Your thermostat is one of the best indicators of your air conditioning system's health.
A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.
Incorrect Thermostat Settings
If the thermostat is not set to the correct temperature or mode, it may not turn on the air conditioning system. To fix this issue, check the thermostat settings and adjust them as needed.
Checking basic thermostat settings, power supply components, and air filter conditions are essential to troubleshoot why an AC unit isn't turning on. More advanced issues requiring professional attention include faulty wiring, a malfunctioning outdoor unit, a bad capacitor, or incorrect thermostat calibration.
Signs of a Faulty Thermostat
AC Refuses to Start or Stops Suddenly: A thermostat that's not working correctly might fail to initiate the cooling cycle or might randomly shut off the AC. This erratic behavior can be due to electrical issues or miscommunication with the AC unit.
Get an Indoor Thermometer
Another way to test your thermostat is to use a thermometer. Place the thermometer in the room and turn on the AC. After a few minutes, check the thermometer to see what temperature it's reading. The temperature should be lower than when you started.
On average, most thermostats last about 10 years, depending on the model, usage, and proper maintenance. However, many people decide to replace their unit sooner to take advantage of new energy-saving technologies.
Yes, many smart thermostats are designed for DIY installation, and manufacturers typically provide step-by-step guides and videos. However, if your HVAC system is older or lacks proper wiring (like a C-wire), the installation might become more complex, and you may need professional help.
Any time you are having an issue with heating and cooling units, such as after a sudden power failure or after your children have had 'control' of the system while you've been away, resetting the thermostat should be the first thing you try when attempting to rectify HVAC system issues.
Replacing a Thermostat. You'll pay between $15 and $300 for the unit in addition to labor ($65 to $100 per hour) to replace an old thermostat with a new one. However, installing a brand-new thermostat is more involved and, therefore, more expensive.
P0128 is an extension of OBD-II code P0 which indicates a problem with your car's coolant thermostat.
There are a number of reasons why your air conditioner might be running but not cooling. It could be an issue with the thermostat, the compressor, or the evaporator coils. Or, it could simply be clogged with dust and debris, which is preventing it from working properly.
Most modern thermostats will have a clearly marked reset button inside the panel. It's usually small and recessed, so you might need a pointed object like a paperclip to press it. For those wondering specifically how to reset air conditioner thermostat models, the process is generally the same.
A malfunctioning thermostat has a harder time maintaining a setting, and may quickly shift temperature settings with no warning. If your central air has a difficult time maintaining the set temperature, even after lowering a setting for a test trial, it could be the thermostat.
The Heater or AC Unit Won't Start.
When the wiring between the thermostat and the air conditioner, furnace, or heat pump comes loose, it will break the connection and leave you cold. Wiring defects can also cause the system to misread temperature settings.
Installation typically takes about 1 hour.
Try checking the circuit breaker box or replacing the batteries. Bad wiring: The thermostat may be unresponsive if the wiring has gone bad. Remove the cover and check inside for loose, detached, or corroded wires. If you spot any problems, contact an HVAC technician for assistance.
If your air conditioner won't turn on, try replacing the batteries if the thermostat is battery operated. Be sure the thermostat is set to “cool” mode and the temperature is set low enough to call for the A/C to come on. Look for a tripped circuit breaker or blown fuse.
The main reasons your AC unit outside is not turning on could be something that has tripped the circuit breaker, something is blocking the fan's airflow, or the condensing unit is damaged. Other potential issues could be the thermostat isn't set correctly or the compressor could be malfunctioning.
Check these issues when the unit won't kick on: Check the thermostat and adjust the settings if it isn't set to Cool and an appropriate temperature setting to call for cooling. Examine the house circuit breakers for the AC unit and reset any tripped breakers. Check the air filter and replace the filter if it's dirty.