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

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

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.