Air Conditioner Controllers have evolved to become more advance in tandem with the advancement made in the field of microcomputer. These days, most window air conditioner and room air conditioner in your homes or offices have electronic controllers in them that make the units more user friendly, intelligent and feature-rich.

Here are some of the typical air conditioner controllers functions. There may be some slight variation depending on the manufacturers of your unit.

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 DC Inverter type of compressor is the latest technology in the market though more costly.

The ON/OFF compressor will 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 ON-OFF cycling of compressor that will reduce its lifespan. 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 manufacturer will have different value). It will only go off when the room temperature drops below 1.25 °C (different manufacturer will have different value).

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 few times of 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 controllers provides a more comfortable cooling to the occupants as the temperature is constant most of the time.

It is also more energy efficient and environmental 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.

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. A temperature setting of 24 C° is a good setting to save energy.

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.

A temperature setting of 28 C° is a good setting to save energy.

In 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 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 hence the humidity of the room will drop. This is basically a dehumidifying function.

FAN mode exists in some model. This mode is hardly used as there is no cooling effect to 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 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 change to Low, Medium, High or Auto. The Auto mode has a built-in intelligent that determine the speed of the fan depending on the room temperature and set temperature. Higher speed is used if the difference between these two temperature is high and lower if low.


Most unit will also have timers that you can use to ON or OFF the unit based on the clock of the remote control. Some simpler unit does not have clock but has delay timers that allow you to set the number of hours elapsed before the unit is turn 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 unit. It is located at the indoor unit and has a high voltage electronic module that ionized 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 a certain hours of operation to ensure its continuous efficiency.

Air Louver

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

Related Links

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 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 thermostat 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.


This is another networking technology that you can use to link up all your equipment.


This Master/Slave serial communication was one of the earliest developed by Modicon.


This is one of the earliest standard communication protocol developed for building automation control including HVAC.


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.


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 controls application.

Editorial Contributors
Alora Bopray

Alora Bopray

Staff Writer

Alora Bopray is a digital content producer for the home warranty, HVAC, and plumbing categories at Today's Homeowner. She earned her bachelor's degree in psychology from the University of St. Scholastica and her master's degree from the University of Denver. Before becoming a writer for Today's Homeowner, Alora wrote as a freelance writer for dozens of home improvement clients and informed homeowners about the solar industry as a writer for EcoWatch. When she's not writing, Alora can be found planning her next DIY home improvement project or plotting her next novel.

Learn More

Roxanne Downer


Roxanne Downer is a commerce editor at Today’s Homeowner, where she tackles everything from foundation repair to solar panel installation. She brings more than 15 years of writing and editing experience to bear in her meticulous approach to ensuring accurate, up-to-date, and engaging content. She’s previously edited for outlets including MSN, Architectural Digest, and Better Homes & Gardens. An alumna of the University of Pennsylvania, Roxanne is now an Oklahoma homeowner, DIY enthusiast, and the proud parent of a playful pug.

Learn More

Learn About HVAC Experts in Your Area