To get cold air from a working A/C system, a working A/C expansion valve is crucial; they can fail without notice. By ignoring expansion valve problems, refrigerant leaks, pressure problems, and corrosion can creep in, and costs can rise fast.
Find out how to identify symptoms of a bad A/C expansion valve early, before your problem gets worse.
What Does an Expansion Valve Do?
To understand what an expansion valve does, it is first important to know about how the A/C system works. All automotive A/C systems use refrigerant as a method to transfer heat out of the cabin by removing heat from the refrigerant. This process starts at a component called the compressor.
With the engine running and the A/C engaged, the compressor pressurizes and pumps vapor refrigerant into the entire system.
After the compressor, the system has a device called a condenser that functions like a radiator, where heat is taken from the refrigerant and dissipated into the air. The refrigerant will also condense into a liquid while in the condenser.
Next, we have high-pressure liquid refrigerant going into this major restriction. The major restriction in the A/C system significantly reduces the pressure of the refrigerant and meters the refrigerant into the evaporator core, which is also seen as a type of radiator.
Depending on the design of this system, the major restriction is either an orifice tube or an expansion valve. If the restriction is an expansion valve type, the expansion valve has a diaphragm and temperature sensing part inside that controls the flow of refrigerant into the evaporator core.
Next, after the evaporator core, the blower motor pushes air through the evaporator core, while heat from the cabin gets transferred into refrigerant, which starts to boil and turns into a low-pressure vapor to get back to the compressor to start the cycle over again.
Lastly, to note, all A/C systems have a dryer to remove moisture from the lines. Systems with an expansion valve use a receiver-drier, while systems with an orifice tube use an accumulator-drier.
Worn-out expansion valves are one of the most common reasons that your A/C is not working anymore.
Signs of a Bad A/C Expansion Valve
Most times, the first sign that something’s wrong with your air conditioning comes in the form of a symptom of a bad A/C expansion valve.
#1. Poor Air Conditioning Performance.
Frequently, that first symptom is a result of your A/C blowing warm air when it used to blow cold air, even after giving the car a few minutes run in the hot sun on a hot day. This indicates that not enough refrigerant is reaching your evaporator.
In the beginning, it may not seem that the airflow is simply not as cold as it used to be, and will ultimately get to the point of warm air coming out of the vehicle’s vents, no matter how low you set the dial on the HVAC.
#2. Inconsistent Air Flow From Vents.
Simply put, the air coming out of your vents will be either too warm or too cold than you are accustomed to and in many cases will alternate back in forth between the two.
If you notice that the temperature inside the vehicle cabin appears to be constantly going from warm to cold, there is a good chance you have a faulty expansion valve.
#3. Air Conditioning Running Continuously.
Another symptom is if your A/C compressor is running continuously. This is due to the expansion valve getting stuck and not opening. This means that the compressor continuously pumps refrigerant into the A/C’s system even though you feel cold.
This is a good point to have your car taken to an auto air conditioning shop to be repaired. To make matters worse, the valves are often deep within your vehicle’s A/C system, and it’s not as easy as just opening a door and slipping a tank of gas into your vehicle.
#4. Frost Forming on A/C Compressor or Vents.
This is the opposite of #1 above. In this case, TOO MUCH refrigerant is being allowed to flow to the evaporator unmetered, which ultimately freezes the evaporator.
In extreme cases, you may even begin to notice a slight frost forming on one or more of the interior vents on the front of the cabin or your windshield.
The A/C expansion valve will often have a  frosty surface to it, which typically guarantees it’s the cause and replacement is warranted.
Cost of A/C Expansion Valve Replacement
Generally, A/C expansion valves can cost around $150 to 350 for the replacement. The valve costs around $50 to $150, and labor costs around $100 to $200, so it’s best to get a few quotes first.
Now that you have an understanding of what can go wrong with your car’s A/C expansion valve, you can get right to the point with your local shop and ask them what to expect in costs, rather than paying for high-dollar labor to simply “see” what is wrong with your A/C.