How Air Conditioner Controllers Work (2024)

Air Conditioner Controllers have evolved to become more advanced in tandem with the advancements made in the field of microcomputers. These days, most window air conditioners and room air conditioners in your homes or offices contain electronic controllers paired with HVAC software that make the units more user-friendly, intelligent, and feature-rich.

Modern controllers also often include advanced features like economical sleep modes, programmable timers, and air-purifying ionizers. Here are some of the typical air conditioner controller functions. There may be some slight variation depending on the manufacturers of your unit.

Related: What are Air Conditioner Motor Applications?

Control Of ON/OFF Compressor

The compressor is the most important component of a vapor compression refrigeration system. The ON/OFF type of compressor used to be popular in the past, but the DC Inverter type of compressor is the latest technology in the market, though more costly.

The ON/OFF compressor will be totally ON or totally OFF, depending on the set temperature and the ambient temperature.

Usually, there is a dead band of about 1.5 °C to 2.0 °C to prevent the ON-OFF cycling of the compressor, which will reduce its life span.

In cooling mode, the compressor will turn ON when the ambient temperature of the room is higher than the set temperature by 0.75°C (different manufacturers will have different values).

It will only go off when the room temperature drops below 1.25 °C (different manufacturers will have different values).

An example of the operation of a compressor in cooling mode.

The disadvantage of this type of compressor is that the temperature range of the space being cooled is too big causing discomfort to the occupants during the time the compressor is either ON or OFF. The other disadvantage is the starting current of easily a few times the steady state current every time the compressor starts.

Control Of AC/DC Inverter Compressor

The DC Inverter or AC Inverter type of control (obviously, the compressor will also be of DC or AC Inverter type) has better control in that it does not have to turn off totally.

The frequency of the rotation of the compressor can vary depending on the load required. Hence, the room temperature of the space being cooled can be very close to the set temperature most of the time, with some slight variation.

This type of air conditioner controller provides a more comfortable cooling to the occupants as the temperature is constant most of the time.

It is also more energy efficient and environmentally friendly as most of the refrigerant used is ozone-friendly. The disadvantage is this type of unit is higher cost compared to the ON/OFF type.

Related: What is Inverter Air Conditioning?

Mode Setting

The mode setting button at the remote control usually enables you to set the mode of operation. It can be set to COOL mode, HEAT mode (if your unit is a heat pump unit), DRY mode, AUTO mode, or FAN mode. Look at the manual provided to see the symbols of each mode.

COOL mode is the default setting that you will use if you want to cool the room upon entering it. The air conditioner will regulate the temperature to achieve the setting temperature of your remote control.

HEAT mode is the mode that you will use when you need to heat up the room during winter. In this mode, the evaporator effectively becomes a condenser and vice versa by using a reversing valve to reverse the flow of the refrigerant.

Today’s Homeowner Tips

A temperature setting of 75 F° is a good setting to save energy.

In the heat pump model, AUTO mode is a mode that will automatically change the mode between COOL and HEAT by sensing the temperature in the room. If the room temperature is low, HEAT mode will operate, and if it goes up to a certain temperature, it will switch to COOL mode.

In the air conditioning model and depending on the manufacturer, the AUTO mode is actually operating in COOL mode but with a lower set temperature to cool down the room quickly before reverting to the set temperature of the user.

DRY mode is a variation of COOL mode where the compressor will cycle on and off (or low speed if inverter model) for a few minutes each, depending on the temperature of the room.

By this cycling, the moisture will be removed from the room — making the humidity of the room will drop. This is basically a dehumidifying function.

FAN mode exists in some models. This mode is hardly used as there is no cooling effect in the room. Only the indoor fan is on. 

Economical Mode

Most air conditioner controllers have the built-in economy or sleep mode function. This function is used when one is going to sleep. When activated using the remote control, the air conditioner unit will raise the set temperature in steps after a period of time. This is because the required cooling will reduce when one sleeps.

Depending on the manufacturer, the set temperature could increase by 1 °C after 1 hour of operation, 1.5 °C after 1.5 hours of operation, and 2.0 °C after 2 hours of operation. Use this mode to save energy.

Fan Speed

Usually, the fan speed can be changed to Low, Medium, High, or Auto. The Auto mode has a built-in intelligence that determines the speed of the fan depending on the room temperature and set temperature. Higher speed is used if the difference between these two temperatures is high and lower if low.

Related: What is a Fan Speed Controller?


Most units will also have timers that you can use to ON or OFF the unit based on the clock of the remote control. Some simpler units don’t have a clock but have delay timers that allow you to set the number of hours elapsed before the unit is turned ON or OFF.

Auto Random Restart

The auto random restart is a feature that will retain the settings of the controls in the event of a power failure. Once power is restored, the air conditioner will restart to its last settings, with the compressor being powered up randomly. This is a good feature to look out for before you purchase the unit.


Ionizer is now a basic feature in most room air conditioner units. It is located in the indoor unit and has a high-voltage electronic module that ionizes the surrounding air with negative ions. These ions will attract dust and other contaminants from the return air to ensure that only fresh and clean air is discharged from the fan coil unit. Take note that the module will have to be changed after certain hours of operation to ensure its continuous efficiency.

Air Louver

Air louver function helps to direct the airflow in the direction of your choice. Most controls have the least up-and-down control of the air. Some units may have left and right louver control as well.

Air Conditioner Remote Controllers

Air conditioner remote controllers work the same way as a TV remote. When you press a button on the remote, it sends a specific infrared code that tells the air conditioner to change settings or turn on and off. The controller inside the AC unit receives the remote’s signals and makes the changes you want.

Most AC remotes allow you to change settings like:

  • Turning the unit on/off
  • Setting the target temperature
  • Adjusting the fan speed
  • Changing the mode (cool, heat, dry, fan only)
  • Setting timers for automatic on/off
  • Activating energy-saving sleep/eco modes
  • Controlling air louvers/vents
  • Turning on ionizers or other air-purifying features

Most modern window AC units and portable air conditioners come with remote controllers so you can adjust them from across the room. On the other hand, most central AC systems don’t come with remotes. However, you can use a smart thermostat along with a mobile app to remotely control it.

Other Controls

Other miscellaneous controls include:

  • Ductless Split Controller – See the troubleshooting guide of the printed circuit board of a split unit.
  • Heatpump Thermostat – Learn how this thermostat can be used to discharge hot air during winter and cool air during summer
  • Heatpump Thermostat Wiring Diagram – See the wiring color code of a typical thermostat.
  • HVAC Symbols – See the electronic HVAC symbols that represent the various components that are used to control the air conditioning systems.
  • Internet of Things – IoT is here to stay, and it is estimated that there will be 50 billion objects with this technology by the year 2020. Find out the impact on the world of HVAC & R.
  • Programmable Thermostat – Use the 7-Day Programmable Thermostat to schedule your air conditioner and save energy at the same time.
  • Types of HVAC Thermostat – Basic descriptions on the types of thermostats that are usually used in HVAC.
  • DC Inverter Air Conditioner – See the simplified block diagram of the split air conditioner using the latest DC inverter technology.
  • LonWorks – This is another networking technology that you can use to link up all your equipment.
  • Modbus – This Master/Slave serial communication was one of the earliest developed by Modicon.
  • BacNet – This is one of the earliest standard communication protocols developed for building automation control, including HVAC.
  • KNX – This is another home and building automation system which is based in Belgium. Design your products in accordance with this standard and enjoy better penetration of your equipment to Europe and the rest of the world.
  • Zigbee – This wireless standard protocol based on IEEE 802.15.4 has low power consumption, low data rate, lower cost, and is suitable for thermostats and other control applications.

Final Thoughts

Your air conditioner controller is a small but mighty computer that works behind the scenes to control your AC unit and keep you comfortable. By monitoring temperature and other conditions, and controlling components like the compressor and fan, it maintains your desired temperature while reducing energy consumption.

Frequently Asked Questions

How does an air conditioner controller know what temperature to maintain?

The controller uses a built-in thermostat that constantly measures the room air temperature. It compares this to the target temperature set you set on your thermostat and turns the compressor on or off to maintain that set point.

Why does my AC compressor turn on and off periodically?

The controller intentionally cycles the compressor to maintain a steady temperature and prevent short-cycling, which can damage the compressor. Most controllers have a “dead band” of 1-2°C where the compressor remains off until the upper limit is reached.

Can I control my air conditioner with my phone instead of the remote?

Many newer AC controllers include Wi-Fi connectivity that let’s you control it with a smartphone app. You can change all the same settings as with a physical remote.

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Reviewed for accuracy, cost data, industry best practices, and expert advice by Jonathon Jachura.

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