Aircon Expansion Valve: What It Does, Common Problems, and What to Watch For

Summary

The expansion valve controls how much refrigerant enters your evaporator coil. It’s the precise metering point that enables cooling. When it fails, your system may undercool, freeze up, or lose efficiency entirely. This guide explains what the expansion valve does, how it malfunctions, and why correct diagnosis is critical before replacing major parts.

What the Expansion Valve Does

Also known as the thermal expansion valve (TXV), this component regulates refrigerant flow from the condenser into the evaporator coil. It ensures that just the right amount of refrigerant enters the coil — allowing efficient heat absorption and consistent cooling. Too much flow? The coil floods. Too little? It freezes.

What Damages the Expansion Valve

• Moisture or contamination in refrigerant

Water, sludge, or metal particles in the system can block or corrode the valve’s internal passages.

• Corrosion or oxidation

Over time, especially in humid environments, the valve body or sensing bulb may corrode — affecting metering accuracy.

• Incorrect installation or retrofit stress

During gas top-ups or major repairs, improper reassembly can affect valve calibration or lead to physical damage.

• Internal wear or mechanical failure

The valve has moving parts — over time, seals or springs can degrade and fail to regulate properly.

⚠️ A faulty expansion valve can look like a compressor or gas issue — only proper testing confirms the source of pressure imbalance.

Repair or Replace?

• Partial blockage or moisture-related issues

Flushing the system and replacing the filter-drier might restore function — but this is only effective if caught early.

• Mechanical failure or corrosion

Most valves must be replaced. They're precision components, and repairs rarely restore proper regulation.

A full pressure and temperature test should always be performed before concluding the valve is at fault.

How to Prevent Expansion Valve Issues

• Use clean, high-grade refrigerant

Contaminated gas is one of the top causes of valve failure — avoid “topped up” units from unknown suppliers.

• Schedule proper system servicing

Routine checks allow early detection of pressure anomalies that may point to valve restriction or flooding.

• Don’t delay when symptoms appear

Reduced cooling, coil icing, or unusual hissing at the indoor unit should trigger a diagnostic — don’t guess.

What Happens If You Ignore It

✖ Coil may flood or freeze due to incorrect refrigerant flow

✖ Compressor can be damaged from liquid refrigerant return

✖ Cooling becomes inconsistent — system may cycle erratically

✖ Efficiency drops and energy usage spikes

Final Word

The expansion valve is small — but critical. It balances the entire cooling process. If your system isn’t cooling properly despite a functioning compressor and fan, this is a key component to check. Accurate diagnosis prevents misrepair and protects the heart of your system.

Suspect your system isn’t cooling correctly?

👉 Request a $30 on-site diagnosis — waived if repair proceeds.