AC Thermostat Not Working? Here’s What You Need To Know

Welcome to our blog, where we’re here to help you tackle common household issues like the ac thermostat not working and keep your home comfortable all year round.

One of the most frustrating problems you might encounter is when your AC thermostat suddenly stops working.

As the summer heat starts to intensify, it’s crucial to have a properly functioning thermostat to maintain a cool and comfortable indoor environment.

In this article, we’ll dive into the possible reasons behind a malfunctioning AC thermostat and provide you with practical solutions to get it back up and running. So, let’s troubleshoot together and restore the perfect temperature control in your home.

Thermostat Not Turning On AC?

thermostat not turning on ac


If your ac thermostat has no power or if it’s not turning on the air conditioner, there could be several possible malfunctions in the HVAC system that can cause the thermostat to go blank and the air conditioner not to work.

Here are some potential problems that require troubleshooting and could be the reason your thermostat is not turning on AC:

  • Power supply problem:

The HVAC system may not be receiving power due to a tripped circuit breaker, a blown fuse, or a power outage. This can result in the thermostat going blank and the AC not working.

  • Thermostat malfunction:

The thermostat itself may be faulty, causing it to go blank and not communicate with the HVAC system. It could be a wiring issue, a damaged thermostat, or a problem with the internal components.

  • Wiring problems:

Loose, damaged, or disconnected wiring can prevent the thermostat from receiving power or sending signals to the HVAC system, leading to a blank screen and no AC functionality.

  • Control board failure:

The control board in the HVAC system manages the communication between the thermostat and other components. If the control board malfunctions, it can cause the thermostat to go blank and the AC to stop working.

  • Transformer failure:

The transformer is responsible for providing power to the thermostat and other components of the HVAC system. If the transformer fails, the thermostat may go blank and the AC won’t work.

  • Blown capacitor:

HVAC systems have capacitors that help start the motors. If a capacitor is blown or damaged, it can affect the power supply and cause the thermostat to go blank and the AC not to function.

  • Faulty compressor:

The compressor is a crucial component of the air conditioning system. If the compressor fails or malfunctions or has any damaged wiring, it can result in the thermostat going blank and the AC not cooling.

  • Low refrigerant levels:

Insufficient refrigerant can cause the air conditioner to stop working properly. If the refrigerant levels are low due to leaks or other issues, it can lead to a blank thermostat screen and a lack of cooling.

  • Faulty fan motor:

The fan motor is responsible for circulating air throughout the HVAC system. If the motor is malfunctioning or has failed, it can prevent the air conditioner from turning on and result in a blank thermostat screen.

  • Blocked or dirty air filters:

Air filters help keep the HVAC system clean and maintain proper airflow. If the filters are dirty or clogged, it can restrict airflow and cause the system to shut down, leading to a blank thermostat display and ineffective cooling.

  • Tripped high-pressure switch:

HVAC systems have high-pressure switches that shut off the compressor if the refrigerant pressure becomes too high. A tripped high-pressure switch can cause the thermostat to go blank and prevent the AC from functioning.

  • Malfunctioning temperature sensor:

The temperature sensor, also known as a thermistor, detects the temperature in the room and sends signals to the thermostat to regulate cooling.

If the temperature sensor is faulty, it can cause inaccurate readings, leading to a blank thermostat display and improper AC operation.

  • Frozen evaporator coil:

If the evaporator coil becomes frozen due to restricted airflow or low refrigerant levels, it can cause the air conditioner to stop working and result in a blank thermostat screen.

These are all the potential road blocks that can hinder the performance of your ac thermostat. Now it’s your job to identify which one is causing the ac thermostat to not work.

Thermostat Set to Cool but AC not Turning On?

If you’re desperately longing for a blissful blast of icy air and your thermostat is set to cool but ac is not turning on or the thermostat itself going blank and the your ac not working…

It’s probably because a low voltage short in your furnace that is causing your AC thermostat to malfunction, here are some troubleshooting steps you can take:

  • Step 1: Safety precautions

Before working on any electrical components, ensure the power to the furnace and air conditioning system is turned off at the circuit breaker or main electrical panel.

ac thermostat not working

  • Step 2: Check thermostat settings

Make sure the thermostat is set to the appropriate mode (cooling) and the temperature is set lower than the current room temperature.

ac thermostat not working

  • Step 3: Inspect thermostat connections

Remove the unit’s cover and inspect the thermostat wiring connections. Ensure they are secure and properly seated on the terminal screws. If any wires are loose or disconnected, reconnect them firmly.

ac thermostat not working

  • Step 4: Check furnace power

Verify that the furnace has power by checking if the blower motor is running when the thermostat calls for cooling.

If the blower motor doesn’t start, there may be an issue with the furnace’s power supply or control board. In this case, it’s recommended to contact a professional HVAC technician.

  • Step 5: Examine low voltage wiring

Inspect the low voltage wiring that connects the thermostat to the furnace control board. Look for any visible signs of damage, such as frayed or exposed wires. If any issues are found, the damaged wires should be repaired or replaced with new ones.


  • Step 6: Test the transformer

The low voltage power for the thermostat is supplied by a transformer in the furnace. Use a multimeter to measure the voltage output of the transformer.

The typical voltage should be between 24-28 volts AC. If the voltage is significantly lower or zero, the transformer may be faulty and should be replaced by a professional.

  • Step 7: Check for short circuits

If you suspect a short circuit, inspect the wiring carefully for any signs of exposed or touching wires. Shorts can cause the low voltage to drop and disrupt the thermostat operation. Ensure all wires are properly insulated and separated from each other.

ac thermostat not working

  • Step 8: Inspect control board and relays.

If none of the previous steps have resolved the issue, the problem could lie with the furnace’s control board or relays.

Inspect these components for any visible signs of damage or burnt connections. If any issues are found, it’s best to consult an HVAC professional to repair or replace the faulty parts.

Remember, when dealing with electrical components and troubleshooting HVAC systems, it’s always recommended to consult a qualified technician if you’re not comfortable or experienced in working with electricity. Safety should always be the top priority.

Thermostat Clicks but AC does not Turn On

To determine whether your thermostat is faulty or if there’s something wrong with the ac. You can use the alligator jumper clips method to test it out.

  • Step 1: Turn off the power

Start by turning off the power to your AC system at the circuit breaker. This step ensures your safety while working with electrical components.

  • Step 2: Locate the thermostat

Identify the thermostat unit in your home. It is usually mounted on a wall and controls the temperature settings for your air conditioning system.

  • Step 3: Remove the thermostat cover

Depending on the model, you may need to remove a cover to access the wiring terminals. Carefully detach the cover by unscrewing or gently pulling it off.

  • Step 4: Identify the wiring terminals

Inside the thermostat, you’ll find multiple terminals labeled with letters or symbols. Common labels include R (power), Y (cooling), W (heating), G (fan), and C (common).

  • Step 5: Identify the thermostat wires

Each terminal has a corresponding wire attached to it. Take note of the wires connected to the R and Y terminals. These are typically responsible for powering the AC system and controlling the cooling.

  • Step 6: Prepare the alligator jumper clips

Get two small alligator jumper clips and attach them to the exposed ends of the R and Y wires. Make sure the clips securely grip the wires to establish a good connection.

  • Step 7: Reapply power

Turn on the power to your AC system at the circuit breaker.

  • Step 8: Observe the AC system

With the jumper clips in place, observe your AC system’s behavior. If the thermostat is functioning correctly, you should hear the indoor blower start running, and the outdoor condenser unit should kick on.

  • Step 9: Check for cooling

Set the thermostat to a temperature lower than the current room temperature. If the thermostat is working properly, you should feel cool air coming from the vents within a few minutes.

  • Step 10: Remove the jumper clips

After verifying the functionality of your thermostat, turn off the power at the circuit breaker again and carefully remove the alligator jumper clips from the R and Y wires.

  • Step 11: Replace the thermostat cover

Put the thermostat cover back in place, ensuring it fits securely.

Final Thoughts

In conclusion, when your AC thermostat is not working, it can be frustrating and uncomfortable, especially during hot summer days. However, by following the steps outlined in this blog post, you can determine if your thermostat is the culprit.

Using small alligator jumper clips can help you diagnose any potential issues. Remember to turn off the power, locate the thermostat, identify the wiring terminals, prepare the alligator jumper clips, observe the AC system, and finally, remove the clips.

These steps allow you to test the functionality of your thermostat and verify if it’s the source of the problem. If you’re uncertain or encounter difficulties, it’s always best to seek professional assistance from an HVAC technician.

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