If your car’s A/C system isn’t keeping you cool like it used to, a faulty expansion valve might be to blame. We often see this overlooked component cause a surprising amount of discomfort especially during the heat of summer. Let’s break down what the expansion valve does, how to recognize the symptoms of a failing one, and what it’ll take to get things working properly again.

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What Is an Expansion Valve and What Does It Do?

Your vehicle’s air conditioning system relies on several key components working together to keep the cabin comfortable. One of those is the expansion valve (or in some systems, an orifice tube). Its job is to regulate refrigerant flow into the evaporator core by reducing pressure, allowing the refrigerant to expand and cool before it absorbs heat from your cabin air.

The expansion valve can prevent proper cooling of the cabin when it fails.

Here’s a quick step-by-step of the process:

1. The compressor pressurizes refrigerant vapor and sends it to the condenser.
2. The condenser removes heat from the refrigerant and turns it into a high-pressure liquid.
3. The liquid refrigerant reaches the expansion valve, where the pressure drops and the liquid begins to expand.
4. This low-pressure refrigerant then enters the evaporator core, where cabin air passes over it, transferring heat out of the air.
5. The refrigerant then turns back into vapor and returns to the compressor, completing the cycle.

In systems with an expansion valve, a temperature-sensing bulb and internal diaphragm control how much refrigerant is allowed through—helping maintain the optimal performance of your A/C system.

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Common Signs of a Bad Expansion Valve

When the expansion valve starts to fail, it can significantly reduce A/C performance—or even cause damage to other parts of the system. Here are the top symptoms we see in our shop:

1. Warm Air from the Vents

One of the most common complaints we hear is that the A/C is blowing warm air. If the expansion valve is stuck closed, it restricts refrigerant from entering the evaporator core. If it’s stuck open, it floods the core, which also disrupts cooling. Either way, you’re left sweating behind the wheel.

2. Frost Buildup

Too much refrigerant flow can cause the evaporator core to flood and ice over, especially near the outlet. Alternatively, if the valve is clogged or stuck closed, you may see frost forming on the valve itself, indicating improper refrigerant flow.

3. Refrigerant Leaks (Oil or Dye Buildup)

A failing expansion valve can also leak. If your system has been serviced with UV dye, you might notice green or yellow residue near the valve. Even without dye, oily buildup in that area could mean refrigerant is escaping.

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Cost to Replace an Expansion Valve

Wondering how much this repair might set you back? On average, replacing an expansion valve runs between $150 and $400 depending on your vehicle make and model. The part itself is relatively inexpensive, but most of the cost comes from labor. The A/C system must be evacuated, the valve replaced, and then recharged all of which takes time and requires professional equipment.