How to Fix a Faulty Expansion Valve in a Constant Temperature and Humidity Test Chamber

Source：LINPIN Time：2025-04-27 Category：Industry News

A constant temperature and humidity test chamber consists of multiple components, and any malfunction can disrupt testing. Previously, we discussed troubleshooting methods for other issues. Today, we focus on expansion valve failures.

To resolve expansion valve problems, first identify the root cause. Common issues include:

Irregular refrigerant supply (fluctuating flow)
Excessive subcooling or superheating

constant temperature and humidity test chamber
These problems are often related to the thermal bulb, primarily due to two reasons:

1. Broken Capillary Tube in the Thermal Bulb
If the capillary tube is damaged, the refrigerant charge inside leaks, preventing accurate signal transmission to the expansion valve’s actuator.

2. Incorrect Thermal Bulb Installation
Improper positioning during assembly can lead to malfunction.

Solutions
① For a Damaged Capillary Tube
Repair or replace the thermal bulb (requires professional servicing).
② For Incorrect Thermal Bulb Installation
Correct the installation position:
The thermal bulb head should face downward or horizontally.
It must be installed below the valve diaphragm’s upper chamber, close to the evaporator and away from the compressor suction port.
Avoid vertical installation—it should be mounted on the horizontal section of the evaporator’s outlet pipe.
Additional Guidelines:

If the thermal bulb is installed higher than the diaphragm chamber, bend the capillary tube into a U-shape to prevent liquid refrigerant from entering the chamber.
For horizontal pipes with a diameter > 7/8″:
Install the bulb below the pipe’s centerline, at a 45° angle (3 o’clock position).
For pipes < 7/8″:
Install it at the top (1 o’clock position).
Avoid mounting at the bottom—this reduces sensitivity, causing excessive refrigerant flow and unstable supply.
By following these steps, you can effectively troubleshoot and resolve expansion valve issues in your test chamber. Regular maintenance ensures optimal performance and extends equipment lifespan.

Previous article: Moving Forward Together to Achieve Greater Heights: Linpin Instruments Renews Partnership with Siemens

Next article: Summary of the 9 Test Levels for Rain Test Chambers

News Recommendation

25.03

What safety precautions should be taken when using a high and low-temperature test chamber?

A high and low-temperature test chamber is designed to simulate natural climatic conditions to test the high- and low-temperature resistance of products or materials under alternating temperature changes.

25.08

The Cleaning and Maintenance Secrets of Constant Temperature and Humidity Test Chambers: Have You Mastered Them?

In many production workshops of enterprises, constant temperature and humidity test chambers are often indispensable pieces of equipment. However, many operators tend to overlook the daily cleaning of these devices during use, leading to a rapid accumulation of grease and dust on the equipment.

24.07

Share: Safety tips for the use of test chambers

Safety for any test chamber is very important, now the equipment are set up to protect the measures, in addition to these self-protection warning, in the usual use of equipment in the process also need to pay attention to the following points.

25.03

Two Types of Separators in High-Low Temperature Test Chambers: How Much Do You Know?

High-low temperature test chambers are equipped with separators, which come in different types.

25.09

Five-Dimensional Analysis of Error Traceability and Precision Control in Salt-Spray Testing

Salt-spray corrosion testing is one of the most frequently used and fastest accelerated methods for evaluating the corrosion resistance of materials and their protective coatings. In a test chamber a salt solution is atomized by compressed air into a uniform fog that is continuously or intermittently sprayed onto specimens in a sealed, temperature- and humidity-controlled space.