In the simplest terms, a thermostatic expansion valve is responsible for controlling the amount of refrigerant that is put into the HVAC system’s evaporator. Without an expansion valve, the refrigerant would not be able to properly change states from a liquid to a gas, which is how a system produces cold air. Let’s take a look at how the thermostatic expansion valve works.
The Purpose of a Thermostatic Expansion Valve
To understand how the thermostatic expansion valve works, it’s important to know the basics of how a cooling system works. There are four main components to a cooling system, including a compressor, evaporator, condenser, and throttling device.
To produce cooled air, warm air enters the system, where it’s blown over the evaporator coil. The evaporator coil is very cold and absorbs the heat from the air passing over it. This cools the air and warms the evaporator coil, which changes the refrigerant from a liquid to a gas. The cool air is blown into the ducts to be distributed through your home. The refrigerant inside of the evaporator is constantly being put through a loop between the compressor, condenser, and evaporator to maintain cold refrigerant at the evaporator.
Once the refrigerant is warmed in the evaporator and turned into a gas, it returns to the compressor. Inside the compressor, the gaseous form of refrigerant is compressed between two solid objects. This increases the temperature and pressure of the gaseous refrigerant before it’s sent to the condenser.
As the superheated vapor refrigerant enters the condenser located outside your home, the outdoor air absorbs the heat from the refrigerant. The temperature of the refrigerant is decreased, and it changes back to a liquid state. This liquid refrigerant is very cold and returns to the evaporator, where it starts the process again.
In order to control the pressure inside of the evaporator and the entire loop, a throttling device must be in place. This is where the thermostatic expansion valve comes in. After the refrigerant leaves the condenser, it must first pass through this device before it enters the evaporator.
A thermostatic expansion valve works by reducing the pressure of the liquid refrigerant that enters the evaporator. When the refrigerant is changed into its gas form, it’s called the superheat. By controlling the pressure of the liquid refrigerant entering the evaporator, a steady rate of superheat exiting the evaporator can be achieved. This creates an efficient process of creating cooled air, and this process controls the amount of pressure inside the system.
It’s important to note that the thermostatic expansion valve does not control the temperature of the evaporator. It only controls the pressure of the incoming liquid refrigerant. The temperature of the evaporator is based on the evaporating pressure, which is based on several factors, such as the capacity of the compressor.
What Happens When a Thermostatic Expansion Valve Malfunctions?
Two things can happen when a thermostatic expansion valve malfunctions. The valve can either become stuck open or closed. If the valve gets stuck too far open, it will basically flood the system with too much liquid refrigerant. This results in low superheat. When the valve gets stuck too far closed, the opposite happens, and you will end up with not enough superheat.
Either way, it results in your system not being able to produce an adequate amount of cooled air to meet your needs. It also causes the system to work inefficiently. Both of these issues result in increased energy bills and wear and tear on your system.
These types of failures are usually a direct result of contaminants such as dirt or moisture in the system. This is one reason why regular HVAC maintenance is so important. When technicians perform a tune-up on your system, they will clean all of the internal parts of your system and ensure there is no moisture buildup.
There are other things that can lead to failure of the thermostatic expansion valve, including improper installation of certain parts. This is why you should only hire experienced and certified technicians to install and maintain your HVAC system, such as those from Underwood AC LLC.
Trust the Experts
At Underwood AC LLC, we’re a full-service heating and cooling provider offering comprehensive HVAC repair, installation, and maintenance. We serve the residents of Davenport and the surrounding areas. We also offer a full range of indoor air quality, ductwork, and pool heating solutions. Contact us today to learn more about our services or to schedule an appointment.
