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My Thermostat Clicks but AC Does Not Turn On

a thermostat

Nothing is more comforting than the clicking sound of the thermostat when it’s hot out. This should mean that cool air is on its way out to relieve you of the heat. But it can be alarming when nothing follows after the click. It might be a sign that there’s something wrong with your air conditioner.

Reasons Your Thermostat Clicks but the AC Does Not Turn On

You don’t have to worry if your AC isn’t switching on despite the thermostat clicking. Most of the time, there is a simple problem behind it that you can solve yourself. However, some issues are more complicated and require the expertise of HVAC professionals. They can have your AC up and running as soon as possible.

Dirty Air Filter

A clogged air filter is the most common culprit behind this issue. Filters purify the air before it travels around your home. Over time, dust, dirt and pollen clog the filter and restrict airflow to the AC system. That will make it harder for your AC to turn on and cool the air. To avoid this issue, it’s helpful to know how often to change the air filter in a house. It’s generally recommended to clean or replace the filter every 60 to 90 days.

Incorrect Thermostat Settings

Adjust the settings if your thermostat clicks but the AC does not turn on. The temperature setting on your thermostat should be low enough to trigger the AC. Likewise, your thermostat temperature should be high enough if you want the heater to come on.

Faulty Thermostat

If your AC fails to start after replacing the air filter and adjusting the thermostat settings, your thermostat might be faulty. It is usually a broken relay system that causes a thermostat to malfunction. A relay is the communication channel between the AC and thermostat, signaling for cold airflow. Here are ways to troubleshoot a faulty thermostat:

  • Check the relay wiring and tighten any loose connections. Check for signs of damage, too.
  • Switch off the thermostat’s breaker. Wait a couple of minutes before turning it back on. The thermostat might be faulty if it doesn’t turn on after the reset.
  • Observe if your thermostat is making any new sounds. If the clicking noise is louder than usual, that could be a sign of a malfunctioning thermostat.

Never replace a thermostat on your own. Improper installation can damage your air conditioning unit. Contact an HVAC specialist if you need a new thermostat. The technician will get the job done right.

Faulty Capacitor

Another thing you should check up on if your AC isn’t turning on is the capacitor. It is the unit’s power source, storing energy to start the compressor. If a buzzing sound accompanies the clicking of the thermostat, that is a possible indicator of a broken capacitor. The buzzing is the compressor trying to run without the electric charge it needs from the compressor. Never try to replace your AC’s capacitor by yourself. It is a dangerous task that you should leave to an HVAC expert.

Faulty Control Board 

For your AC to function, there must be a stable connection between the thermostat and the control board. When you turn on the thermostat, it will send a signal to the control board. The control board will then trigger the AC to turn on. But if the control board is malfunctioning, you will hear a clicking sound from the thermostat, but your AC will remain off. Again, replacing a control board is a job best left to the HVAC pros.

Faulty Contractor

A contractor is another essential connection between the thermostat and your AC. It is responsible for turning the AC on and off, triggering the compressor inside. If the contractor is malfunctioning, your AC can’t receive the signals from the thermostat. The thermostat will produce a loud clicking noise, but the AC will still be off.

a home with an ac compressor that is making noise

Why Is My AC Compressor Making Noise?

Is your AC compressor making noise? Specific sounds can mean different problems. Some issues are easy to repair, while others are more complex. When in doubt, err on caution and call an HVAC specialist. Compressors store an electrical charge and can be dangerous to repair or replace yourself.

Debris or Loose Parts

Many parts inside an AC unit can come loose over time because of wear and tear. If you hear rattling or banging noises, that is a sign that something has come undone and is bouncing around inside the unit.

Debris can make similar sounds. The outdoor portion of your AC unit is more susceptible to this problem because of its exposure to the elements. Leaves, branches and other debris can get stuck inside and cause rattling and banging noises when you turn the unit on.

Faulty Fan Blades or Motor

If you hear helicopter-like noises from your AC compressor, there might be a problem with the condenser fan. The blades are near the compressor and could be hitting it, explaining the alarming sound. It might also be that the fan is loose or something is stuck between the blades. You must address these issues before the fan causes a more severe problem.

Faulty Compressor

A grinding noise is indicative of a worn-down or overworked compressor. It is a common problem among older AC units that aren’t well-maintained. The beat-up piston pin might be working extra hard to contain the refrigerant, producing the sound you hear. Repairing or replacing a compressor that isn’t working requires the expertise of an HVAC pro. But if it is a complex problem, they might tell you to replace your AC unit.

Electrical Issues

High-pitched buzzing or humming noises could mean your AC has an electrical problem. There might be an exposed cable or faulty or grounded wires. The production of electromagnetic fields is a silent process, so there’s an issue if the compressor makes loud noises.

Pressure Buildup or Refrigerant Leak

A hissing noise accompanied by a noise that sounds like screaming is a sign of building pressure. High pressure inside an AC compressor could mean the thermostatic expansion valve is leaking or faulty. It could also be a sign that the high-pressure sensor is malfunctioning. Whatever the case, turn the AC off immediately if you hear this sound. Wait until an HVAC technician has repaired it before turning it on.

On the other hand, a hissing and bubbling noise is a sign of a refrigerant leak. It is another complex problem that needs the attention of an HVAC professional.

a living room

Why Your AC Fuse Keeps Blowing

Nothing is more frustrating than an AC fuse that keeps blowing in the summer. While there are many possible causes for this issue, the number one culprit is a dirty air filter.

Not only does the filter keep the air in your living space clean, but it also keeps the AC running smoothly. It has to work much harder to push clean air through if the filter is dirty or clogged. That can cause your unit to wear down prematurely, explaining why the breaker keeps tripping. Generally, replacing the filter at least once every three months is best.

Low refrigerant levels can also cause the AC fuse to blow out. It is the refrigerant’s job to absorb heat from the air and cool it down when it flows along the evaporator coils and compressor. When there is not enough refrigerant, it can cause unnecessary strain on the AC and trip the breaker. Other possible reasons are a malfunctioning capacitor or damaged electrical wiring.

Here are some maintenance tasks you or an HVAC professional can regularly perform to keep your AC unit running smoothly:

  • Check your evaporator coil annually and clean it if needed. Dirt on the evaporator coil can restrict airflow and hamper its ability to absorb heat.
  • Use a fin comb on your AC’s coil fins. This tool will arrange the fins back into their original position, allowing for better airflow.
  • Insert a stiff wire into your AC’s drain channels to unclog them.
  • Cover your AC in the winter. That way, it is protected from harsh weather and debris.

The Bottom Line

Air conditioners can make life at home comfortable, even on the hottest summer days. But, it can be worrying when the thermostat clicks but the AC does not turn on. Homeowners can face other AC problems, including loud compressor noises and blowing fuses.

Fortunately, professional HVAC technicians can address all these issues. With their tools, knowledge and experience, they can get to the root of the problem and have your AC running smoothly again.

ABC Can Resolve Your Thermostat Problems

Thermostats are complicated and issues can arise for a number of reasons. Instead of trying to diagnose these issues yourself, contact ABC Home & Commercial Services. Our pros will efficiently diagnose and repair the HVAC problem and get to work on fixing it. We even provide preventative AC maintenance so we can catch potential problems early.

Tom Riggs

Tom Riggs is the Division Manager for Mechanical Services, overseeing sales and operations for HVAC, Plumbing, Electrical, Appliance Repair and Water Quality for all ABC Austin branches. He joined ABC in 2014. Before ABC, he was an HVAC Service Technician, HVAC Comfort Advisor/Sales and Operations Manager. Tom attended Universal Technical Institute. He's an avid outdoorsman and enjoys country living with his wife and two sons.

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