How Do You Diagnose a Commercial Refrigeration System by Reading Its Operating Pressures?
2026-11-11
A commercial refrigerator rarely fails without warning. Before the compressor locks out or the box drifts warm, the gauges move first. Reading suction and discharge pressure as temperatures, not as numbers to match against a sticker, turns a service call into a short and logical diagnosis.
Convert Pressure Into Saturation Temperature
Every refrigerant has its own pressure-temperature curve, so convert the low-side reading into suction saturation temperature and the high-side reading into discharge saturation temperature. Use the refrigerant on the unit plate: R290 on most AILIPUSH reach-ins, R404A or R23 on low-temperature blast freezers. A gauge value copied from another system proves nothing.
Compare Suction With Box Temperature
On a reach-in holding 1°C to 4°C, an evaporator running 5°C to 8°C colder is working normally. Far below that range suggests a starved coil; close to or above box temperature suggests excess load or an overfeeding valve. Superheat at the evaporator outlet should sit near 3°C to 5°C on a thermostatic expansion valve.
Compare Head Pressure With Ambient
Discharge saturation temperature on an air-cooled condenser typically sits 5°C to 11°C above the air entering the coil. Higher suggests a dirty coil, failed fan, recirculated hot air or a cabinet too close to a wall. Lower can mean low charge, or a condenser over-cooled in winter.
Benchmark and Log
Absolute values vary by model, ambient and load, so compare against a second unit of the same model. The GN Series ALPS-1.0L2FGN holds 1°C to 4°C on R290; its freezer twin, ALPS-1.0L2FDGN, runs -22°C to -18°C, both with a thermostat accurate to 0.1°C. Record suction, discharge, box and ambient temperatures at every visit: one reading is a moment, five are a trend.
AILIPUSH has 15 years of experience in commercial refrigerator manufacturing. We offer factory-direct sales and specialize in commercial air-cooled refrigeration equipment. Contact us today for more information!
Product reference: GN Series Double Doors Upright Chiller & Freezer (ALPS-1.0L2FGN / ALPS-1.0L2FDGN), ailipush.com.
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