Check the wire connections between the AC unit and thermostat, especially if your AC is not responding to thermostat adjustments. Damaged or loose cables can interfere with communication between these devices.
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.
Replace Dead Batteries
While some thermostats are hardwired, many use batteries or have batteries as a backup power source. Dead batteries are one of the most common reasons a thermostat may fail to turn on the air conditioning system, leading to a loss of connection and inability to activate the HVAC system.
If the wiring between the thermostat and the air conditioning system is faulty, the system may not turn on. This can happen if the wiring is old or if it has become damaged over time. To fix this issue, you may need to call a professional HVAC technician to inspect and repair the wiring.
HVAC System Suddenly Quits Working
Try replacing the batteries, then check for a blown fuse or tripped breaker in the electrical panel. If the thermostat is still unresponsive, make sure the breaker is shut off and remove the cover.
Sometimes, when the room temperature doesn't match the thermostat setting, the problem could be dirt buildup on its interior parts. A dirt coating around the inner components may create excess heat and cause the thermostat to give the wrong readings.
Locate the sensor, which is a small, round component usually positioned near the bottom of the thermostat. It may be labeled as “sensor” or “thermistor.” Using a soft brush or a can of compressed air, carefully clean the sensor to remove any dust or debris that may have accumulated on its surface.
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.
Switch the thermostat to the off position. Locate the breaker that powers your HVAC system and turn it off. Wait 30 seconds and turn the breaker back on. Turn your thermostat back on and confirm it has reset properly.
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.
Press the reset button. Most models require you to hold the button down for 3-5 seconds before releasing. Restore power to your AC. Restore power to the unit at the circuit breaker, and make sure the unit is set to “on” and your thermostat is set to “cool.”
Air Conditioner Won't Turn On
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. If you're satisfied that the system is getting power, a faulty thermostat may be preventing the system from turning on.
In this case, the homeowner should check the wiring connections and the position of the sensor, which should be near the evaporator coil but not touching it. Adjusting the sensor is easy. Simply bend the wire that holds it in position.
It could be your thermostat, your air filter, a problem with the condenser or compressor, or it may just be time to replace the unit, especially if it's over 10 years old.
Check Your Circuit Breaker
Locate your main circuit breaker and switch it back to the "On" position. Wait 30 seconds and turn on your air conditioner again. If it still doesn't work, you'll need to call a professional for help.
Make sure the outside unit is turned on (there's probably a switch near the unit). If the outside unit has a separate circuit breaker, check your circuit box and make sure it hasn't been tripped. A more serious issue if the outside air conditioning unit's not working is a broken compressor, capacitor or fan.
If your thermostat is not working, you may want to check your AC filters. The filters are responsible for trapping dirt and dust particles. If the filters are not working, the thermostat will not be able to function correctly. When the air filters are dirty and clogged, air will struggle to pass through them.
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.
No, the coolant temperature sensor cannot be reset.
The engine coolant temperature sensor, or ECT is just a resistor affected by temperature—nothing's being stored on it and it has no software. The ECT works by receiving a signal from a computer called the engine control unit, or ECU.
The average cost for an Engine Coolant Temperature Sensor Replacement is between $406 and $448. Labor costs are estimated between $97 and $122 while parts are priced between $309 and $325. This range does not include taxes and fees, and does not factor in your unique location. Related repairs may also be needed.