One question splits this in half
Is the box at setpoint?
At setpoint and still running — the system is capable and nothing is telling it to stop. This is a control fault.
Above setpoint and still running — the system is being told to run, correctly, and cannot get there. This is a capacity fault.
Those two lead to entirely different parts of the equipment, so establish which one you have before anything else.
If it is at setpoint
Contactor welded
The contacts have fused and the power path never opens, whatever the control says. Test: turn the thermostat up well above box temperature. If the compressor keeps running, the control circuit is no longer in charge. This needs attention the same day, because a cooler running continuously will ice its evaporator and give you a second fault on top of the first.
Control failed closed
Mechanical thermostats fail this way as they age. Electronic controller relays weld like any other.
Sensor reading warm
Nothing is broken; the controller simply believes the box is warmer than it is and keeps calling for cooling. Drift, a bad connection, or a sensor sitting in the return air near a door.
If it is above setpoint
The system is running flat out and losing. In rough order of how often we find each:
- Condenser blocked. Head pressure up, capacity down. Always check this first because it is the most common and the cheapest.
- Charge low from a leak. Capacity falls with charge.
- Evaporator iced or dirty. The coil cannot transfer heat into the refrigerant.
- Infiltration load. A failed gasket or a door that will not latch means the system is cooling the kitchen through a gap, continuously.
- Compressor losing efficiency. Valves worn. It runs, it draws current, it pumps less than it should. This is an end-of-life symptom.
- Load genuinely exceeds capacity. More product, more door openings, more heat sources than the system was sized for. Nothing is broken; the business outgrew the box.
What it is costing while you decide
A compressor is usually the largest electrical load in a kitchen after the cooking line. The difference between running sixty percent of the time and running continuously is close to a seventy percent increase in that system’s energy consumption, every day, until it is resolved. On a system that was already going to need attention, the energy difference alone often covers the repair within a few months.
The seasonal version
Continuous running that appears in July and disappears in October is almost always the condenser. A coil that is partly blocked has enough capacity in mild weather and runs out of headroom when the ambient climbs. If your box has a summer problem and a winter non-problem, clean the condenser before investigating anything more expensive — and then put it on a schedule, because a coil that got that bad once will do it again.
The useful thing to measure
If you can, log run time for a day. Many electronic controllers record it; otherwise a note every half hour of whether it is running will do. Knowing it runs ninety-five percent of the time rather than sixty tells a technician more than any description, and it gives you a before-and-after measure so you can see whether the repair actually worked rather than taking anyone’s word for it.
Questions we get asked
What run time is actually normal?
Fifty to eighty percent across a day is typical for a well-matched walk-in in normal service. Higher than that in a heatwave or after a large warm product load is expected temporarily. Continuous running on an ordinary day is not.
Is continuous running actually harmful?
It is harder on the compressor than normal cycling, it costs noticeably more in energy, and on a cooler it can drive the coil below freezing continuously so it ices over and makes the capacity problem worse. It is also usually a symptom of something else that is getting worse.
The box is at the right temperature and it still never stops. Why?
The control is not opening the circuit. Either the thermostat or controller has failed closed, the sensor is reading warm, or the contactor contacts have welded together so the power path never breaks.