What Does a Thermostat Sensor Do on an Air Conditioner

What Does a Thermostat Sensor Do on an Air Conditioner

, by Thrive Agency, 6 min reading time

Air conditioners ensure our comfort during scorching summers, becoming indispensable to modern life. Behind the efficient operation of these machines is an essential component, the thermostat sensor. This component plays a crucial role in maintaining the desired indoor temperatures while significantly impacting your home's energy efficiency.

If you require compatible thermostat sensors for your cooling unit, look no further than Value Controls. We provide top-of-the-line sensors and other essential components to keep your HVAC systems in tip-top shape.

Below, we’ll cover the function of your AC's temperature sensors, help you understand how they work, the types available, and how they can optimize your comfort and boost cost savings.

How Does a Thermostat Sensor Work?

A thermostat sensor functions as a temperature-sensitive device for heating and cooling systems. It monitors the ambient temperature in your premises using a bimetallic strip or electronic sensor. When the temperature exceeds the desired set point, it activates your cooling system, maintaining the desired temperature.

These sensors provide a crucial interface between users and HVAC systems, ensuring energy efficiency and comfortable indoor conditions. Whether you're considering purchasing a thermostat or repairing an existing one, understanding how these sensors work is fundamental for effective temperature control and cost-effective HVAC operation.

Sensor Classification

Your air conditioning unit can have any of the two existing types of thermostat sensors:

1. Contact Temperature Sensor

A contact temperature sensor is a device designed to measure the temperature of objects or surfaces through direct physical contact. It typically consists of a temperature-sensitive element, such as a thermocouple or resistance temperature detector (RTD), housed in a protective casing.

The sensor's probe accurately detects and records temperature. Contact temperature sensors are commonly used in industrial and scientific applications, where precision and reliability are essential for processes like quality control, research, or equipment maintenance.

2. Non-Contact Temperature Sensors

Also referred to as infrared temperature sensors or pyrometers, non-contact temperature sensors are devices that can measure an object's temperature without any direct physical contact. These sensor types work by detecting the infrared radiation emitted by an object.

A thermostat sensor in this class can help measure the temperature of hot, moving objects that are difficult to access safely. Non-contact temperature sensors find applications in various industries, such as manufacturing, automotive, and medical, where precision and non-invasive temperature measurement are critical. 

Types of Thermostat Sensors

Your AC can have any of the following thermostat sensors installed:

Bi-Metal and Gas-Filled or Liquid Thermometers

There are two main types of thermometers commonly used in different cooling systems:

  • Bi-metal thermometers 
  • Gas-filled or liquid thermometers

Bi-metal thermometers consist of two metals bonded together in a coil or strip, expanding or contracting when the temperature changes. This movement is then translated into a temperature reading.

Gas-filled or liquid thermometers, on the other hand, use a gas (such as nitrogen) or a liquid (like mercury, for instance) that expands or contracts with temperature variations, causing the fluid level to rise or fall, which is used to measure temperature. Gas-filled and liquid thermometers often offer greater accuracy and sensitivity than bi-metal thermometers, making them suitable for more precise HVAC systems.


The thermostats in an AC unit are contact temperature sensors that employ a bi-metallic strip composed of two dissimilar metals, like copper, nickel, aluminum, or tungsten. The key feature of these sensors is the difference in the coefficient of linear expansion between the two metals.

When exposed to heat, this difference causes the strip to bend or deform mechanically, which is used to detect temperature changes. This bending movement is the fundamental mechanism that triggers the AC system to turn on or off, helping maintain the desired temperature in space by controlling the heating or cooling processes. Bi-metallic strip thermostats have been widely used for their reliability and cost-effectiveness in HVAC systems.


Thermocouples are temperature sensors with two metal wires or strips joined at one end. When exposed to a temperature gradient, these wires generate a small electrical voltage due to the Seebeck effect, which is directly proportional to the temperature difference.

This voltage is measured and used to accurately determine the junction's temperature. Thermocouples are widely used for their robustness, versatility, and vast temperature range capabilities. This feature makes them valuable in various applications, from industrial processes and scientific research to monitoring and controlling temperature in furnaces, ovens, and HVAC systems.


Thermistors are temperature-sensitive resistors made of ceramic materials, typically composed of metal oxides. These electrical components exhibit a significant change in resistance in response to temperature variations, with resistance decreasing as temperature increases (negative temperature coefficient - NTC) or increasing as temperature rises (positive temperature coefficient - PTC).

Thermistors are highly sensitive and precise, allowing for accurate temperature measurements. They find extensive use in industrial applications such as temperature control, thermal protection, and temperature compensation. They can be installed in electronic circuits, HVAC systems, and a wide range of consumer and other industrial devices.

Applications and Use Cases

Thermostat sensors are used for a variety of applications in both residential settings and industrial and commercial locations. Here are some of the most common applications of these devices today:

  • Medical Industry: In medical applications, thermostat sensors are vital for maintaining precise and stable temperatures in incubators, vaccine storage, patient temperature monitoring, and laboratory equipment, ensuring the integrity and effectiveness of medical samples, drugs, and vaccines.
  • Residential Applications: In-home applications, thermostat sensors are primarily used for regulating heating and cooling systems, ensuring comfortable indoor temperatures and energy efficiency.
  • Vehicles: Thermostat sensors are essential for controlling cabin temperature. They monitor the interior climate and help regulate the HVAC system to maintain the desired comfort level, ensuring occupants stay comfortable during various driving conditions.

Trust the Reliable Thermostat Component Supplier

When you're in the market for a new thermostat sensor, it’s best to know which type is compatible with your HVAC system. Value Controls has specialists who can help you determine your needs. Shop for wireless and other types of thermostats on Value Controls or call us at 1-800-584-9901.


Blog posts


Forgot your password?

Don't have an account yet?
Create account