A/C Thermostat Problems & Solutions | Day & Night Air Conditioning, Furnace, & Plumbing

When something goes wrong with your air conditioner, the real problem may actually be the thermostat. This article answers FAQs about thermostat problems:

  • What causes thermostat issues?
  • What are the most common issues with smart thermostats?
  • How can you tell when your thermostat has problems?

The air conditioner indeed does most of the heavy lifting, but the thermostat is the one calling the shots. It determines when the A/C turns on, when it turns off, and how long it runs. So when thermostat problems appear, it affects the entire cooling system. What are the most common A/C thermostat problems in Phoenix, AZ, and surrounding metro cities?

What Are the Most Common A/C Thermostat Problems?

1. Thermostat or A/C Doesn’t Have Power

Sometimes, the A/C isn’t working because the thermostat isn’t turned on. You wouldn’t believe the number of times this is the reason for thermostat issues. It’s possible for kids to “accidentally” bump the on/off button out of curiosity.

If batteries power your thermostat, the batteries may have died. Another common issue is that the cooling system may have tripped a circuit breaker, leaving the A/C and the thermostat without power.

To troubleshoot this A/C thermostat problem, just go in order. First, check the power button. If that doesn’t work, try replacing the batteries. Lastly, go to the breaker box and see if there’s a tripped breaker. Any of these things can restore power and get the thermostat working again.

2. Air Conditioner Suddenly Stops Working

What if the thermostat display is working correctly, but the air conditioner still isn’t working? First, make sure it’s actually set to “cool” (or “heat” depending on what you’re looking for). Also, double-check the circuit breaker problem we mentioned above.

If the circuit breaker isn’t the issue, your thermostat may have loose wiring. It’s getting power, but it’s not communicating correctly with the central cooling unit. This type of problem is very different from an air conditioner that has been having a lot of problems and finally gives out. When the thermostat is the problem, the A/C will be working fine one minute and nothing the next minute.

We don’t recommend trying to check or resolve wiring issues yourself. It’s always better to let our certified electricians and HVAC professionals fix the problem.

3. HVAC System Not Cooling Enough

Another common issue is that the actual room temperature doesn’t seem to match up with the setting on the thermostat. You may end up turning the dial down further and further to try to stay comfortable.

Some homeowners think this is normal, and they may adjust the temperature taking into account the difference. This is a bad idea because it wastes energy and only puts a Band-Aid over a bigger problem.

Fortunately, calibrating the thermostat is part of preventative maintenance checkups for your air-conditioning system. As long as you schedule a tune-up every six months or so, your family should never have to worry about this problem.

4. Short Cycling

This term refers to the air conditioner turning on, running for less than a minute, and then turning off again. When the system is short cycling, it repeats this routine over and over. Running like this uses up a lot of energy, leading to a big electricity bill at the end of the month.

This problem has a lot of possible causes. There may be a sensor issue or calibration problem. Other common causes of A/C short cycling include a dirty air filter and an HVAC system that is too big for your house.

5. AC Running Constantly

This may not be a problem. If you recently upgraded your HVAC system to an energy-efficient model, it’s actually normal for it to run 80–90% of the time. Modern A/Cs have variable-speed compressors that can run at lower speeds, longer, and save electricity by not turning on and off.

Also, if it’s a really hot day in Phoenix, AZ, and the surrounding metro cities, then it’s natural for the A/C to run more than usual. Air conditioners have to work pretty hard to keep up with a heatwave. You may want to raise the temperature a little so the system can rest a bit.

On the other hand, older thermostats can get stuck. If you think there’s a thermostat problem, turn off the HVAC system to prevent overheating. Then, call us right away.

6. Smart Thermostat Malfunction

Don’t get us wrong — smart thermostats are amazing. But, like any type of digital equipment, they can have glitches sometimes. There may be a software bug or a communication issue. Check your internet connection and Wi-Fi.

Another issue that can happen with smart thermostats is that they’re not getting enough power. This is usually only an issue with DIY installation. For smart thermostats, your home needs a 24-volt C wire for power. Otherwise, they can “steal” power from the HVAC, making it malfunction.

We’re happy to take care of the installation. Our professional electricians know exactly what they’re doing, which keeps costs low and prevents expensive problems down the road.

What Causes Air Conditioner Thermostat Problems?


Is the thermostat located in a place where it gets sunlight? That can cause problems because it heats the temperature sensor incorrectly. The thermostat thinks it’s hotter inside than it actually is, so it keeps running constantly. This can damage the system.

The best solution is to call our pros to move the thermostat to a different wall. A temporary fix is to cover the thermostat with a towel or close the curtains to keep sunlight away.


You know how dusty some parts of Phoenix, AZ, can be. After a while, dirt and dust can build up outside and inside the thermostat. This dust layer does the opposite of sunlight on the sensor. It prevents the sensor from heating up, tricking the air conditioner into thinking the room is cooler than it really is.

That’s why you end up fighting so hard to get the temperature in your home where you want it. It’s a good idea to dust your thermostat every time you dust the other furniture.

Leveling problems

This mainly happens with older thermostats. When it’s not perfectly level, temperature readers aren’t measured correctly. You can adjust this using a carpenter’s level. Honestly, the best solution these days is to upgrade to a smart thermostat instead.

Improper installation

This is the most significant cause of thermostat issues that we’ve come across. If the previous homeowners tried to install the thermostat themselves or hire an inexperienced “handyman,” so many things can go wrong. An incorrect install often causes wiring problems, temperature issues, and short cycling of the HVAC unit.

The solution for most of these problems is straightforward. Only trust certified HVAC experts to install or fix air conditioning components, including the thermostat.

Are you looking to upgrade an older thermostat to an energy-efficient smart thermostat? Is your thermostat having problems? Call us at Day & Night Air Conditioning, Heating & Plumbing in Phoenix, AZ, and surrounding metro cities. We can help any time, 365 days a year.

Featured Image: Commercial RAF/Shutterstock

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