Properly Positioning the Sensing Bulb of a TXV

Sensing bulb placement is important

The correct placement and installation of the thermostatic expansion valve (TXV) sensing bulb is important to its overall performance and reliability. An incorrectly installed or placed sensing bulb can lead to several different types of system problems. Below are some general installation concerns and tips to follow when installing a TXV:

• Always follow the manufacturer’s installation guidelines. They take precedence over any of these general recommendations.

• For suction lines less than 7/8 inch, place the sensing bulb at the 12 o'clock position on the suction line leaving the evaporator.

• For 7/8 inch to 1 5/8 inch suction lines, place the sensing bulb at the 10 or 2 o’clock position.

• For suction lines greater than 2 inches, place the sensing bulb at the 4 or 8 o'clock position.

• Never place the sensing bulb at the 6 o’clock position.

• If a TXV uses a gas-charged maximum operating pressure (MOP) power element, the sensing bulb needs to be wrapped to ensure it reads true pipe temperature.

• Be sure to locate the sensing bulb on a free-draining suction line.

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• Locate the sensing bulb at least 18 inches from the point where the suction line exits the cabinet.

• The sensing bulb should never be located on a suction line header.

• Do not locate the sensing bulb on a vertical riser after a trap.

• Avoid locating the sensing bulb on any fittings.

• Never locate a sensing bulb directly on a suction line trap.

• Make sure the sensing bulb is securely fastened to the suction line. Use a metal clamp to secure the sensing bulb to the suction line and do not use tape or wire ties.

• Do not attach the sensing bulb until after the valve is brazed in and the pipe is cooled.

Excerpted and reprinted from Troubleshooting Tips for Servicing Refrigeration Systems by Joe Marchese with Leo A. Meyer, one of the books in the Indoor Environment Technician’s Library series published by LAMA Books.

Publication date: 2/8/2016

KEYWORDS: TXV (thermostatic expansion valve)

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Joe Marchese is an author, instructor and HVACR service contractor. He can be reached at joe@koldcraft.com.

For over 30 years, Leo A. Meyer has written and published training materials for the HVAC industry. His books cover a wide range of topics, including heating and cooling, indoor air quality, sheet metal work, electricity basics, safety, and others. For more information, visit www.lamabooks.com.