Maintenance Tips for Thermostatic Expansion Valves

In refrigeration systems, the thermal expansion valve (TX valve) serves as the critical "gatekeeper" of refrigerant flow, precisely controlling the amount of refrigerant entering the evaporator to ensure efficient and stable operation. While UnicoSystem's TX valves are renowned for their reliability and performance, even these high-quality components can malfunction due to various factors, with valve blockage being the most common issue.

When a TX valve becomes clogged, many immediately consider replacement. However, proper cleaning and maintenance can often restore the valve's functionality and extend its service life. This comprehensive guide provides step-by-step instructions for safely and effectively cleaning thermal expansion valves in UnicoSystem and other refrigeration systems.

Understanding TX valve maintenance begins with recognizing its fundamental role in refrigeration systems. As an automatic control valve, the TX valve adjusts refrigerant flow based on evaporator load changes to maintain optimal operating conditions.

The TX valve operates on thermodynamic principles, with key components including a sensing bulb, capillary tube, diaphragm, valve needle, and seat. The sensing bulb, installed at the evaporator outlet, detects refrigerant superheat. When superheat increases, the bulb's internal fluid expands, transmitting pressure through the capillary tube to open the valve. Conversely, decreased superheat causes the valve to close, reducing refrigerant flow.

Common causes of TX valve obstruction include:

• System contaminants: Metal particles, welding slag, oxides, and moisture circulating through the system
• Improper brazing techniques: Poor welding practices during installation or repairs
• Inadequate vacuum procedures: Residual moisture reacting with refrigerant
• Substandard refrigerant quality: Impure or moisture-containing refrigerants
• Compressor issues: Oil entering the refrigerant system and forming deposits

Recognizable signs of TX valve blockage include:

• Reduced cooling capacity
• Evaporator frost formation
• Compressor overheating
• Abnormal system pressures
• Frequent compressor cycling

Before any maintenance, safely recover all system refrigerant using professional recovery equipment. This critical step ensures personal safety and environmental protection.

Key considerations:

• Never vent refrigerant to atmosphere
• Follow all local regulations and industry standards
• Consult professionals if unfamiliar with recovery procedures

After refrigerant recovery, carefully disassemble the TX valve:

• Locate the valve at the evaporator inlet
• Remove the cap nut to access internal components
• Reference valve schematics to avoid damage

Safety note: Always disconnect power before servicing.

Cut the liquid line externally using a tube cutter (never a hacksaw) to minimize metal debris. Position wet cloths or vacuums to capture particles.

Connect plastic/rubber tubing to the valve's center feed tube and apply nitrogen pressure to flush out debris. All pressure should discharge through the cut liquid line.

Important: Use proper regulators to avoid excessive pressure.

Apply pressure from the cut line (opposite normal flow direction) to dislodge any remaining particles trapped between the needle and seat.

Thoroughly examine and clean the cap, spring, and needle/seat assembly. Remove any debris or corrosion using appropriate cleaners that won't damage components.

Reassemble components in correct sequence, ensuring proper alignment. Apply minimal refrigerant oil to moving parts before securing the cap nut (avoid overtightening).

Install a liquid line filter-drier and sight glass upstream of the valve. For heat pump systems, use bidirectional filter-driers compatible with refrigerant flow reversal.

Use electronic leak detectors to verify all connections. Address any leaks immediately through proper tightening or seal replacement.

Perform deep vacuum evacuation using the triple vacuum technique:

1. Pull vacuum to 500 microns
2. Break vacuum with dry nitrogen
3. Repeat at 250 microns
4. Final evacuation below 100 microns

This method effectively removes moisture while preventing ice formation in small-diameter tubing.

Regular TX valve maintenance offers significant benefits:

• Cost savings versus replacement
• Extended component lifespan
• Restored system efficiency
• Preventative problem avoidance

When performing maintenance, always use proper tools and safety equipment. For complex situations, professional assistance is recommended.

This comprehensive cleaning guide provides a proven method for restoring TX valve functionality in UnicoSystem and other refrigeration systems. Proper maintenance not only resolves immediate performance issues but also prevents future problems through systematic care and component protection. By following these procedures, technicians can maintain optimal system operation while minimizing unnecessary part replacements.