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Identifying a Bad Expansion Valve in Your AC System

A thermostatic expansion valve, or TXV, is the part of your air conditioning system responsible for maintaining a steady flow of refrigerant to the evaporator using a sensing bulb. The TXV is critical for keeping you cool and collected, which is why you’ll want to have it fixed as soon as possible.

Check For a Bad Expansion Valve

If your expansion valve fails, it’s likely the TXV sensing bulb has lost its charge. This can leave you with a high superheat, low suction pressure, and insufficient cooling. The sooner you can identify if a failed TXV is the root of your problem, the quicker you can cool off some stress and have your AC system back in tip-top shape.

How to Check For a Bad Expansion Valve

  • Turn off your air conditioner at the thermostat. All ice has to thaw before a technician can diagnose the cause.

  • Look at your thermostat to see if it's maintaining the temperature you set. If it's not, it could mean there's an issue with your air conditioner.

  • Depending on the type of thermostat you have, you might be able to see the humidity level right on the screen. If you can't, you can test humidity using an indoor humidity gauge. If the reading is over 60% relative humidity, you could have an issue with your air conditioner.

    To test using an indoor humidity gauge, leave the gauge in the area being tested and make sure it's not disturbed. Since levels can vary from room to room, we recommend using multiple gauges to test different rooms at the same time. Using more than one gauge will give you a more accurate overall picture.

  • Locate the sensing bulb in your air conditioning unit, near the evaporator outlet. Make sure it is connected tightly to a suction line. If you can move the bulb, it is not properly connected.

    While you're at it, make sure that the insulation is intact on the bulb as well.

    CAUTION: Don't kink or pull on the copper capillary line.

  • Check the lines inside the AC system for any kinds of blockage, kinks, or ice. A frosted line indicates that your TXV valve could be failing.

  • If there are no signs of other issues in the system, the TXV could be broken. To confirm that your TXV is faulty, test the valve. Check the evaporator coil and remove the TXV's sensing bulb from the suction line. Check the subcooling, superheat and pressures again. If there's no change, that's a further indication of a TXV problem. Another test is to put the sensing bulb in ice water and checking the pressures superheat, and subcooling again.

    CAUTION: This is a job for a trained HVAC technician. Refrigerants operate at very high pressures.

If a bad expansion valve doesn't seem to be the problem, consider other reasons your AC isn’t running smoothly.

What to Do If You Have a Bad Expansion Valve

Once you’ve determined you have a bad expansion valve, call an HVAC professional to repair the issue and get your cool and crisp air back in a flash. With a completely failed expansion valve, TXV replacement may be necessary.

If you’d like a helping hand in the expansion valve troubleshooting process, one of our Remote Assist Experts can guide and help you identify the next steps towards a working AC system.

NOTE: This content is for informational purposes only, and HomeX and its affiliates disclaim all liability related to it. If you decide to perform any tasks based on this information, you assume all risks, including the risk of loss or damage to property or personal injury.

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