Pflugerville TX: TXV Restriction vs Low Refrigerant Diagnostic Case
Location: Blackhawk (ZIP 78660) • Diagnostic Second Opinion • Reading Time: 4 Minutes
The Problem: System Running Constantly After Sunset
A homeowner in Blackhawk near FM 685 contacted our dispatch desk for a diagnostic second opinion. Their 4-ton R-410A split system ran non-stop from 4 PM until midnight, failing to cool below 78 degrees despite 80-degree outdoor night temperatures. A previous contractor had recommended adding 4 pounds of refrigerant without taking psychrometric readings.
Blindly adding refrigerant to a restricted system causes liquid floodback, which destroys compressor reed valves and washes lubricant from crankcase bearings.
Our Texas TDLR Class A technician connected digital manifolds to measure true superheat and subcooling simultaneously.
Diagnostic Proof: Superheat vs Subcooling Mathematical Method
Low-side suction pressure measured 98 PSI (saturated temperature of 31°F), with a suction line temperature of 57°F, indicating an abnormally high superheat of 26°F. High-side liquid pressure measured 385 PSI with a liquid line temperature of 98°F, calculating a subcooling reading of 16°F, significantly higher than the 11°F nameplate target.
If the system were truly leaking refrigerant, subcooling would drop below 5°F because insufficient liquid would stack in the condenser.
The elevated 16°F subcooling proved that plenty of refrigerant was present, but was mechanically trapped upstream of a restricted thermal expansion valve.
Resolution & Performance Verification
The technician recovered the full factory 8.5-pound R-410A refrigerant charge, cut out the sludge-clogged OEM thermal expansion valve, brazed in an upgraded bolt-on TXV with dry nitrogen flowing, replaced the liquid line filter drier, evacuated the system to 380 microns, and returned the verified refrigerant charge.
Upon restart, superheat dropped to 11°F and subcooling stabilized precisely at 10.8°F, delivering 54-degree register air throughout the home.
Homeowners in Blackhawk, Falcon Pointe, or Round Rock seeking accurate diagnostic second opinions can contact our emergency AC repair team 24 hours a day.
Need a Precise AC Diagnostic Second Opinion?
Texas TDLR Class A technicians provide digital testing across Pflugerville TX.