What Does an AC Expansion Valve Do & How Does It Work? (2025)

Air conditioners keep your home cool during those hot summer months. However, these marvels of modern technology rely on countless parts to function, including the essential air conditioning expansion valves. What does an AC expansion valve do exactly?

Here’s more from Leith Heating & Cooling, the team to call for reliable AC repair in Elgin, IL. This post discusses the air conditioning expansion valve, how it works, and how to identify a broken one.

What Is An Air Conditioner Expansion Valve?

Air conditioning expansion valves are incredibly important, lying at the heart of any air conditioning system. It is a pressure valve that regulates refrigerant flow through the air conditioner to enable heat transfer. So, it effectively lets your unit’s refrigerant absorb outdoor heat to generate cool air.

From a mechanical standpoint, it is quite fascinating to see how your air conditioner expansion valves will automatically adjust the amount of refrigerant flowing into the system’s evaporator coil. Without the valve, the refrigerant would flood into the evaporator coil to cause serious damage to your air conditioner. That’s why if an air conditioner expansion valve wears out, clogs, or sustains damage, it can lead to many different problems, such as:

• Reduced cooling capacity
• Mechanical malfunctions
• Coil failure
• Motor issues and more

Types of Air Conditioner Expansion Valves

There are many different types of air conditioner expansion valves, each varying in type, size, and style. However, the four common types of valves you’ll encounter include the following:

Float Valve

Float valves rely on actual floats that rest inside the liquid refrigerant. They use two floats: one for low pressure and another for high pressure.

• The low-pressure float maintains a constant refrigerant level in the evaporator.
• The high-pressure float regulates refrigerant levels in the condenser.

Float valves use a unique pair of floats to maintain consistent refrigerant levels. Other types of air conditioner expansion valves only have one working component, whereas these more complicated valves have two. Here, maintenance from professionals like Leith Heating & Cooling is essential to keep your unit’s refrigerant levels balanced and the cooling functioning efficiently.

Automatic Expansion Valve

With automatic expansion valves, there’s a self-regulating mechanism or pressure-actuated diaphragm. These valves detect refrigerant flow and adjust it as needed. While this flexibility has benefits, it sometimes struggles to keep up in systems with rapidly changing refrigerant flow.

Thermostatic Expansion Valve

The third type of valve is the thermostatic expansion valve, which adjusts the refrigerant flow rate depending on the temperature. As the evaporator warms up, the flow rate increases, and when the evaporator cools down, the flow rate decreases. It’s a great system if you want to focus on more efficient cooling or heat distribution.

Part of what makes these devices so uniquely brilliant is how they use temperature-sensing bulbs to detect temperature changes. When your unit’s temperature changes, the bulb either contracts or expands. This simple yet effective mechanism helps regulate refrigerant flow depending on changes in both pressure and temperature.

Capillary Tube

Capillary tubes are a small yet effective expansion valve option, particularly suitable for portable and window air conditioners. These tubes filter out dirt, debris, and other particulates from the unit’s refrigerant supplies. However, these valves struggle to cool larger units, which is why industry professionals like Leith Heating & Cooling will only pair capillary tubes with smaller units.

Signs of a Bad Expansion Valve

So, you understand the basic function of these components, but what does an AC expansion valve do when it is going wrong? Here are some common signs that will alert you to a faulty expansion valve so that you can catch the problem early.

Strange Noises

If you own an air conditioner, you’ve probably heard it occasionally make light humming or buzzing sounds. While these noises are normal, other strange noises, such as whistling or rattling, are not.

For example, air conditioners experiencing expansion valve issues make whistling noises as they struggle to handle pressure effectively throughout a system. The whistling or squeaking often means your system is leaking refrigerant, an urgent problem. When left unaddressed, refrigerant leaks cause your air conditioner to freeze and may cause health problems.

Ineffective Cooling

Your air conditioner’s cooling process relies heavily on its expansion valve. While expansion valves don’t directly control your unit’s temperature, they control the refrigerant flow that makes the entire cooling process possible. So, broken pressure relief valves can spell trouble for your air conditioner.

In particular, if you notice warm spots throughout your home or a lack of cold air coming from your vents, there’s a good chance your air conditioner’s expansion valves aren’t working.

High Energy Bills

Malfunctioning air conditioning units spike energy bills, so if you can’t understand why your unit’s energy consumption is through the roof, consider whether your unit’s pressure drop valves are working. Faulty pressure valves strain the air conditioner, which makes it use more electricity and drives up your utility expenses.

If you want to be sure, work with local HVAC experts like Leith Heating & Cooling to help you rule out possible causes of heating bill increases. They can give you advice, issue repairs, and suggest improvements that could streamline your air conditioning’s energy efficiency long-term.

How Much Does It Cost To Repair an Expansion Valve?

Your expansion valve’s repair and maintenance costs will depend on countless factors, including whether you need a quick fix or an entirely new valve installed. If you want to minimize the potential repair costs, be sure to ask about regular expansion valve maintenance services to keep it in good knick.

That said, HVAC professionals like Leith Heating & Cooling will also be able to tell you whether the system will be better off replacing your air conditioner’s expansion valve instead of repairing it. This decision makes sense if your unit’s valves are old or beyond repair.

Professional HVAC Services in Elgin, IL

What does an AC expansion valve do when functioning optimally? It provides the perfect balance for your Elgin home. Count on the licensed, bonded, and insured technicians from Leith Heating & Cooling for a new air conditioner quote or urgent repairs—call 847-534-8686 today!