Walk-In Cooler Starved Evaporator Diagnosis

Convert the pressures to temperatures first.

• Suction 45 psig R-404A ≈ 19–20°F saturation. Box is 45°F, so evaporator TD ≈ 25°F against a 10°F design - the coil is far colder than it should be, which only happens when it is starved of liquid feed.
• 25°F superheat at the evaporator outlet confirms starvation. A properly fed coil runs 6–10°F superheat.
• 22°F subcooling is abnormal; normal is roughly 5–12°F. High subcooling with high superheat is the signature of a restriction between the condenser outlet and the evaporator: liquid backs up in the condenser (raising subcooling) while the evaporator gets too little refrigerant (raising superheat). Prime suspects are a plugged TXV inlet screen, a restricted or slugged liquid-line filter-drier, a kinked or undersized liquid line, or a TXV power element that has lost its charge.
• Discharge 245 psig ≈ 111°F saturation at 95°F ambient = 16°F condensing approach. Higher than ideal but not the primary cause; it is consistent with the greasy coil reducing heat rejection.
• The clear sight glass does not exonerate the liquid line: the glass sits upstream of the drier and the valve, so a restriction downstream of it still reads clear.

Confirmation, in order:

1. Pump down and isolate the liquid line. Measure temperature across the filter-drier and across any suspect fitting; a measurable ΔT across the drier is a restriction until proven otherwise.
2. Remove and inspect/clean the TXV inlet screen; verify the power head, bulb charge, bulb location and insulation, and that the external equalizer (if used) is clear.
3. Compare valve capacity to the actual evaporator and refrigerant - a valve that is correct on paper but at the wrong rated capacity for R-404A will behave this way too.
4. Only after the liquid path is proven clean, weigh in the charge per the nameplate and set superheat at the design box condition.

Why not add gas: the system is already showing more subcooling than it should, which means liquid is stacking in the condenser. Adding charge compounds that, raises discharge pressure on an already-fouled condenser, and does nothing for a starved evaporator. If the restriction is later cleared, the system is now overcharged and at risk of liquid floodback to the compressor. Charge is set by weight or by the manufacturer's subcooling method - never by 'top it off until the glass clears.'

Secondary corrections:

• Clean the condenser with a coil-safe degreaser and rinse, verify fan blade, rotation, and airflow clearance on the mezzanine. Re-check condensing approach after cleaning; it should drop toward roughly 10–15°F.
• Verify the evaporator fan(s), defrost termination and frequency, door gaskets and closers, strip curtains, and the product load (a warm product pull-down is not a refrigeration fault).
• Check compressor amps against nameplate RLA and confirm oil level; a starved coil runs hot suction gas and can overheat the compressor.

Proof of performance, recorded:

• Box and product temperature; ambient at the condenser.
• Suction and discharge pressures converted to saturation temperatures; superheat at the evaporator outlet and at the compressor; subcooling at the condenser outlet; condensing approach.
• Compressor amps versus nameplate; running time and pull-down rate over a documented period with the doors closed.
• Post-repair superheat within the manufacturer's target at 35°F box, and pull-down from 45°F to 35°F within a stated time.