Refrigerant contamination is one of the most damaging conditions in commercial DX systems, especially in buildings with equipment that has been serviced repeatedly over many years. Moisture, acid and particulate matter undermine metering performance, weaken lubrication and shorten compressor life.

These issues often show up in DFW properties with aging equipment that has undergone repeated leak repairs. Each repair is another chance that contaminants enter the circuit.

How Contamination Gets Into Commercial Systems

Lines left open to the atmosphere during service work pull in moisture, and inadequate evacuation leaves vapor trapped in the piping. Air intrusion is common during leak repairs on older equipment, especially when work occurs in tight chases or rooftop conditions with wind and debris. Improper brazing creates copper oxide that flakes off and travels through the system.

A second group of contaminants forms internally, such as when a compressor burnout distributes acid through the oil and refrigerant. Unless the circuit is fully cleaned, that acid continues attacking metal surfaces long after the new compressor is installed.

Older systems also accumulate debris from past repairs, failed filter driers or coil replacements, which easily migrates toward metering components.

How Contamination Disrupts TXVs and Metering Performance

TXVs react quickly to contaminants. Particulates settle at the orifice and restrict flow, creating unstable superheat that affects the entire system. Wax from overheated POE oil binds internal surfaces and slows pin movement, and acid scoring reduces the valve’s ability to modulate during load changes. These conditions mimic symptoms of low charge or inadequate airflow, which is why intermittent performance problems in older RTUs often trace back to contamination rather than refrigerant quantity.

Why Compressor Oil Quality Declines in Contaminated Circuits

POE oil absorbs moisture readily, and once water enters the system it triggers chemical changes that weaken the oil’s lubricating properties. As contamination increases, oil becomes more acidic and less effective at protecting bearings and scroll sets.

Miscibility problems also appear: degraded oil may not return properly from long evaporator circuits or extended line sets. Facilities with long piping runs are particularly susceptible, as any drop in oil quality magnifies the challenge of maintaining consistent lubrication.

Signs of declining oil quality include higher compressor amp draw, elevated discharge temperatures and early winding fatigue. These indicators show up even when refrigerant charge and airflow appear normal.

Compressor Failures Driven by Contamination

A contaminated circuit can destroy multiple compressors if the underlying problem is not addressed. After a burnout, acid remains inside the system without proper flushing, drier replacement and deep dehydration. The new compressor inherits the same environment and often fails in a similar pattern.

Signs that continued contamination is responsible for compressor failures include:

• Repeat burnouts
• Bearing washout and increased mechanical noise
• Restriction at the metering device leading to high head pressure
• Discharge temperature spikes during peak-load operation

When these symptoms appear together, the refrigerant circuit is usually the root cause.

Components Beyond the Compressor That Suffer Damage

Contamination affects many components, not just metering devices and compressors:

• Reversing valves can stick when copper plating forms inside the pilot passages
• Solenoids and check valves fail when debris settles in critical openings
• Coils exposed to acidic refrigerant corrode internally, reducing heat-transfer efficiency long before leaks appear

Identifying Contamination in the Field

Technicians rely on more than pressure readings to confirm contamination:

• Oil samples reveal moisture levels, acid presence and early signs of metal wear
• Moisture indicators at the liquid line help show whether the system has dehydrated properly
• Superheat patterns, valve response and temperature splits across coils are tracked during varying load conditions to identify restrictions

How Contaminated Systems Are Restored

Corrective work depends on severity. Typical steps include:

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• Extended evacuation to remove moisture
• Installing oversized filter driers and replacing them after cleanup
• Flushing or replacing line sets when particulate load is high
• Replacing TXVs or coils that remain restricted after dehydration

Tom’s Commercial focuses on restoring reliability without unnecessary component replacement. Call 817-857-7400 to schedule a field evaluation to confirm whether moisture, acid or particulate contamination is driving your system issues.