Expansion Valve: Operation And Problems

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Expansion Valve: Operation And Problems

Expansion Valve: Operation And Problems

26 November 2019
, Blog

The thermostatic expansion valve (TXV) is a critical part of many modern air conditioning (AC) systems. The TXV regulates the flow of refrigerant in the system, which determines the amount of cooling output. Below is an overview of the workings and problems with TXVs.


The TXV is not a single component; rather, it is comprised of four main parts – the sensor, capillary tube, diaphragm, and valve body. The sensor detects the temperature and pressure of the refrigerant, the capillary tube connects the bulb to the diaphragm, and the latter opens and closes to regulate the refrigerant depending on the detected pressure and temperature.

The refrigerant is usually warm, under high pressure, and in liquid form as it enters the TXV. The TXV reduces the pressure of the refrigerant, and low pressure reduces the temperature before the refrigerant flows out of the expansion valve. The cold refrigerant is then able to pick up more heat from the air and cool the house.


The TXV, just like other parts of the AC, can breakdown and interfere with the cooling efficiency of the AC. Below are some of the common TXV malfunctions.

Loose Attachments

The TXV will malfunction if it is not properly attached to the rest of the AC unit. As previously mentioned, the pressure reading is what triggers the opening and closing of the expansion valve. Unfortunately, this pressure reading will be erroneous if the expansion valve is loosed attached. This will be the case because the loose attachment will lead to artificially low pressure, leading to improper valve opening and closing.

Broken Bulb

A TXV has a bulb that acts as the temperature detector for the system. This bulb is relatively delicate and can potentially break. The effect of a broken sensor is erroneous temperature readings, which also interferes with the operations of the TXV and the AC's cooling efficiency.

Low Coolant

Problems in other parts of the AC can also affect the operations of the TXV even if the TXV itself is sound. For example, refrigerant leaks that occur elsewhere (such as the AC coils) will reduce the pressure of the refrigerant throughout the whole AC system, including the TXV. The persistently low pressure of the refrigerant may prevent the TXV from opening as usual, and your AC's cooling ability will be affected.

The TXV is integral to your AC's operations; consult an AC technician as soon as possible if your AC's TXV is acting up. The technician will diagnose the root of the problem and replace it if it has malfunctioned (most TXV problems require replacement).

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Troubleshooting HVAC Issues

About a year ago, I realized that our air conditioner just wasn't cutting it. Our home was constantly hot and humid, even though our air conditioner was running almost all the time. In addition to driving up our energy bill, my entire family was tired of sweating constantly. To resolve the problem, we decided to hire an HVAC contractor to come out and fix the problem. He figured out that our compressor was damaged, and he replaced it for us. After that, our system ran great again. This blog is here for anyone who has ever had trouble diagnosing air conditioning problems.