Home AC Thermostat Not Working? Thermostat Questions?

Do you have a broken thermostat? A digital thermostat with a blank display? Check this list of some of the most common questions we encounter concerning AC thermostats, find your problem in the list below, and scroll down to the appropriate section.
  • How does a thermostat work
  • Digital thermostat is blank
  • How to replace a thermostat
  • Wireless thermostats
  • Air conditioning thermostat setting
  • Thermostat not turning on the heat
  • What is the best thermostat

How Does a Thermostat Work?

ac thermostat not workingRegardless if you have a digital thermostat or an older mercury style thermostat. They both do the same thing, although digital thermostats tend to be more accurate.

A thermostat is just a temperature-sensitive switch. Once the ambient room temperature rises above or drops below the desired set point, the thermostat internal contacts close to direct 24-volt control voltage to the various components of the air conditioning system.

Because the thermostat is sensing the surrounding air temperature of its location, placement is critical. Generally, the thermostat is located on an interior wall within 10 feet of a return vent ( AC vent that pulls air into the system). The reason for this is a more homogenized average air temperature.

Placing a thermostat in the direct airflow of a supply vent ( AC vent that air comes out of ) can skew the temperature reading, causing short cycling of the HVAC system. Placing the thermostat in direct sunlight or another heat source can have the same effect.

The Digital Thermostat Is Blank

Other than the thermostat itself has failed, a blank thermostat means there is no power to the thermostat. Check the batteries. If the batteries are O.K..

A safety mechanism in the system may have interrupted power to the thermostat causing loss of power. For more detail check out this previous blog post - “ Why is my digital thermostat blank.

How to Replace a Thermostat

ac thermostat not working replace thermostatReplacing a thermostat really isn't that difficult. Before you even attempt to replace it is critical that you shut the power off to the handler.

The reason for this isn't so much as you will receive an electrical shock ( its only 24 volts ) but there is a potential for creating an electrical short in the control circuit.

Once the faceplate is removed, take a picture of the existing wiring configuration, label the wiring if needed as a reference for the new thermostat. It is also important that the correct replacement thermostat is purchased.

Is your system a heat pump? Or a straight cool system with electric heat or gas. Does your system have multiple stages of cooling? It makes a difference. of replacing a thermostat with some of the standard color codes for thermostat wiring.

Wireless Thermostats

These thermostats are typically used if a traditional thermostat cannot be used. For example, a difficult location to physically wire or maybe a multiple zone property. In Florida, we have a lot of multi-story condos, with the condenser located on the roof for example.

The condo may be on the 6th floor, but the equipment is a couple of stories up on the roof. If the existing wiring is damaged, This may be an application for a wireless thermostat.

A wireless thermostat uses a receiver and a radio signal. There are limitations, depending on the manufacturer as to how far the radio signal can travel distance wise. This can be affected by the structure, concrete wall, etc.

What is the Best Thermostat Setting?

ac thermostat not working best settingThe best setting honestly is what you are comfortable with. What's the point of having a central AC system if you aren't comfortable in your own house? Energy-wise, the AC setpoint makes a huge difference.

If the air conditioning system is sized correctly, most people are comfortable at 78 degrees with a reasonable humidity level in the house or 68 degrees in the winter. Every degree above that can represent an energy cost of 6 to 8 percent on your energy bill.

A programmable thermostat is a real energy saver if you actually use it. If you have a fixed schedule, at work all day- set the temperature setting up 4 to 5 degrees. If programmed correctly, when you arrive home the house will be at the temperature you like. Some thermostats on the market have an algorithm built in that learns how long it takes to “recover “ temperature-wise to make it even more accurate.

Thermostat not Turning on Heat

In Florida, we don't even use the heat for some years. But when we do get a cold snap, we get swamped with service calls because the heat won’t come on.

Often time it is because the homeowner has replaced the thermostat and it is simply not programmed correctly, a simple dip switch on the back of the thermostat is set incorrectly, or the thermostat itself is the wrong application required for the system.

Make sure whether your system is a heat pump or a straight cool system with electric heat or gas that the thermostat you install is designed for your HVAC system and properly setup. Refer to the owner's manual.

What Brand of Thermostat is The Best?

Which Thermostat Is BestThis is just our opinion, but dealing with thermostat day in and day out we do have a couple of favorite brands of thermostats.

In general, the thermostats that are available at Home Depot & Lowes are definitely a cheaper quality than what most contractors install.

Even though they may carry the name brand of the thermostats listed below, often it is an inferior/different product than what the professionals use.


Honeywell Thermostat

Honeywell makes a ton of different thermostats. Most carry a five-year warranty with the contractor's grade product. They offer a full spectrum of thermostats from the very basic up to the top of the line product.

Really can't go wrong with Honeywell. Honeywell offers a helpline for homeowners if there is a problem during installation.


Nest Thermostat

Everyone knows Nest at this point; they are well marketed. Nest thermostats are sold at home stores and are the same quality that contractors can buy.

There are different models so make sure you choose one that applies. I believe all nest thermostats are wifi capable.

This allows the homeowner to control their system from an app on a phone or computer. The setup is pretty simple; the thermostat walks you through the process step by step.


Venstar Thermostat

Venstar makes a great thermostat. They have models that sync up with Alexa if you have one, the wifi thermostats look great and have a stable app to control from your phone or computer and are easy to set up.

They have models that have full-color LCD screens. Photos can be loaded on the screen if desired and lots of other features. Never have had any problems with Venstar.


Ecobbe Thermostat

Ecobee also makes an excellent stable thermostat. They make a model where Alexa is built into the thermostat itself. They also have an app that walks you through the installation process. Pricing is excellent as well for the level of thermostat you receive.

AC thermostat not working? Need a thermostat installed? Air Zero is a professional 5 star rated HVAC contractor located in Largo Fl. We service all of Pinellas County. Give us a call at


Air Zero Installs AC Thermostat