The walk-in reads 36 at seven in the morning. By four in the afternoon it’s at 40 or 41, and by the next morning it’s fine again. Nothing looks broken, but one busy dinner could put food over the limit.
How the condenser gets rid of heat
A refrigeration system doesn’t really make cold. It moves heat out of the box and dumps it outside through the condenser, the unit with the fan that’s usually on the roof, on a pad behind the building, or in the base of a reach-in. And it can only dump that heat into air that’s cooler than the coil.
On a mild morning that’s easy. On a 95 degree afternoon, with the sun on a black roof and the condenser sitting right on it, the air around the coil can be a lot hotter than the forecast says. Pressures climb and the compressor works harder while moving less heat per hour. A system with plenty of room on a cool day can be right at its limit by mid-afternoon in July. Anything that makes the condenser’s job harder shows up first on those days. A coil packed with dirt, cottonwood or kitchen grease is the big one. Also look for boxes or trash stacked against the unit, a fence or new shed blocking airflow, or two condensers set up so one blows its hot air straight into the other.
More door traffic in the afternoon
Afternoon is also when the walk-in door gets the most use, between dinner prep, late deliveries and someone propping it open while they find a spot for a rack. Warm, humid kitchen air rolls in each time. The kitchen itself is hotter by then too, which matters a lot for self-contained units pulling air from right next to the line.
What to check this week
Go look at the condenser first.
A gray mat of dust on the coil, or a film of grease, means it needs cleaning. We wrote a separate post on cleaning condenser coils, including what you can safely do yourself. Clear out anything stored around it while you’re there.
Inside, check that the door closes on its own and the strip curtain is in one piece. Cool hot food some other way before it goes in the walk-in if you can. If your deliveries come in the afternoon, get the product put away fast and the door shut.
If the box still climbs after the coil is clean and the door’s sorted, have a tech look at it. Low refrigerant and a worn compressor both get worse in the heat, and it’s better to find out in June than in August. Our page on condenser and compressor repair goes into what they’ll check, and a spring maintenance visit gets the coils cleaned before the hot weather shows up.