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Expansion Valve Stuck Closed – Effects and Solutions
Expansion Valve Stuck Closed: Effects & Solutions
Understanding the consequences of a malfunctioning TXV and how to address them
What is an Expansion Valve?
The thermal expansion valve (TXV or TEV) is a precision component in air conditioning and refrigeration systems that regulates the flow of refrigerant into the evaporator. It’s designed to maintain proper superheat at the evaporator outlet, ensuring maximum system efficiency.
AC System Flow Diagram
High pressure, high temperature gas
High pressure, medium temperature liquid
Regulates refrigerant flow
Low pressure, low temperature liquid/gas
What Happens When the Valve Stays Closed?
When an expansion valve becomes stuck in the closed position, it severely restricts or completely blocks refrigerant flow to the evaporator. This creates a cascade of problems throughout the entire AC system, potentially leading to component failure and costly repairs if not addressed promptly.
Immediate Symptoms of a Stuck Closed Expansion Valve
No Cooling
Little to no cold air from vents as refrigerant cannot reach the evaporator to absorb heat from the air.
Low Suction Pressure
Significantly reduced pressure on the low side of the system due to restricted refrigerant flow.
High Head Pressure
Elevated pressure on the high side as compressor continues working against a restricted system.
Evaporator Frost/No Frost
Possible frost buildup near expansion valve or no frost at all on evaporator coils due to refrigerant starvation.
System Impact Comparison
Normal Operation
- Proper refrigerant flow through system
- Balanced high and low side pressures
- Evaporator completely filled with refrigerant
- Correct superheat at evaporator outlet
- Efficient heat absorption in evaporator
- Compressor runs with normal current draw
Valve Stuck Closed
- Little to no refrigerant flow to evaporator
- Very low suction pressure, high head pressure
- Evaporator starved of refrigerant
- Excessive superheat at evaporator outlet
- Poor or no cooling capacity
- Compressor overload and potential damage
Pressure Changes with Stuck Closed Valve
| Parameter | Normal Condition | Valve Stuck Closed | Change |
|---|---|---|---|
| Suction Pressure | 60-70 PSI | 10-20 PSI or lower | Dramatic Decrease |
| Discharge Pressure | 200-250 PSI | 300-400 PSI or higher | Significant Increase |
| Evaporator Temperature | 40°F (4°C) | 65°F+ (18°C+) | Increase |
| Superheat | 8-12°F | 20°F+ | Excessive |
| Subcooling | 10-15°F | Increased | Increase |
Long-Term Consequences
Compressor Damage
Running with low suction pressure causes inadequate cooling and lubrication, leading to overheating and potential seizure.
Electrical System Strain
High head pressure increases compressor workload, causing excessive current draw that can damage electrical components.
Oil Circulation Problems
Refrigerant starvation impedes oil return to compressor, leading to lubrication failure and mechanical damage.
System Contamination
Compressor overheating can break down oil and create acids that contaminate the entire system.
Diagnosis and Solutions
Proper Diagnosis
Use manifold gauges to check for very low suction pressure and high head pressure. Measure superheat (will be excessively high) and check for temperature drop across the valve.
Valve Replacement
In most cases, the best solution is to replace the faulty expansion valve. Ensure the replacement matches specifications for your system.
System Cleaning
Install a new filter-drier to capture any contaminants and prevent future valve problems. Consider flushing the system if contamination is severe.
Refrigerant Management
Recover existing refrigerant, repair/replace valve, evacuate system thoroughly, and recharge with correct amount and type of refrigerant.
Professional Attention Required
Expansion valve issues require professional HVAC technician expertise. Attempting repairs without proper training and equipment can lead to further system damage, personal injury, or voided warranties.
Key Takeaways
A stuck closed expansion valve creates a refrigerant starvation situation that prevents proper cooling and puts excessive strain on the compressor. The combination of low suction pressure and high head pressure can quickly lead to compressor failure—the most expensive component in an AC system.
If you suspect expansion valve problems, contact a qualified HVAC technician immediately to diagnose and address the issue before it causes further damage.